Wednesday, April 28, 2010

The Jackson Creek lava delta and the 'two' Bogus lavas

The upper photo is a slightly less common shot (for our group at least) of the Jackson Creek lava delta. We usually see this from the river and look mainly at the south-facing exposure. This is the north-facing exposure. Since I took this picture a while back, I have actually walked out on that outcrop to get a gigapan image of Jackson Hole. In so doing, I found that the two conspicuous lava flows are separated by the lacustrine silt package indicated in the previous post. No surprise given that the outcrop is right across the trib canyon from the much better exposure shown in that post. The difference in quality of exposure of the lacustrine silts is controlled by the presence of a thick lag of Bogus Rim lava mantling the surface.

The photo below is the 'classic' view of this outcrop (taken almost exactly two(!) years ago). The lava delta is associated with the lower Bogus lava unit. You can't see the intervening lacustrine silt package, but the Bogus Rim lava at the top is obvious.

Lacustrine sediment between Bogus Rim lava and older Bogus lava

The photo below is looking north across Jackson Creek Canyon on river left. The upper lava is good ol' Bogus Rim, the white stuff is probably lacustrine silt. The little wedge of lava upon which the silt lies is what I call the lower Bogus...but may correspond to the Bogus Point lava (?).

Click on the image to enlarge. The wedge that sits conspicuously below the silt has a couple of companion wedges on the canyon wall below where I am standing. It is clearly inset into the older rocks. Note that the higher wedge that is perched on the silts is a small landslide block of the Bogus Rim lava.

Note also how the lacustrine silt grades abruptly upward into bedded gravel. As the image below attests, some of the light colored fines are interbedded with the trib gravels. The Bogus Rim lava is also capped by the gravels in this outcrop.

Upstream-most remnant of West Crater Lava on river-left

I don't think I ever shared photos from our trip last May. My, how time flies. This is the tiny wedge of lava that survives across the river from the bulk of the flow upstream from Dogleg Bar.

Three distinct basalt flows below Bogus Rim?

This first photo is looking west into a basalt-choked tributary valley just downstream from Iron Point. I recall inferring three major intracanyon flow units here divided by conspicuous breaks. Just throwing it out there for all to consider.

This photo is looking upstream from west side of the river (near Rinehart Mesa) toward and beyond Jackson Hole. The intracanyon flow sequence here is very thick. Possibly three units here as well? The lower shelf right above the talus slope has the 'hackly' texture that we see at the base of the section near Rinehart Creek as well.

Young Basalts in Yeehow-ville: Even more ruminations from Duane!

[all...once I clone myself, I will add annotated images to these discussions...Kyle]

The Junction of Crooked Creek, and the Owyhee River

The air photos help to see more details in the vicinity of where Crooked Creek joins the Owyhee River. This is an area that Kyle, Cooper, and I have briefly mused over. I think I see three (3) different young basalt flows in this area. There is an odd “comet-shaped” lobe of lava which enters Sect. 31, T30S, R41E located in the SW corner of the Owyhee Butte quad from the SSW. There it has an omni-directional scarp which rolls over at about 3640’, which is lower than adjacent surfaces to the N and SE of the lobe. This lobe seems to be a northerly extension of the lower of the double outcrop that Bill Hart argon dated just N of the State Wayside Park, at 1.25 ± 0.28 Ma. The younger of the two E-facing scarps that Hart dated at 0.91 ± 0.36Ma, is located just a half mile to the W of this odd shaped outcrop, and forms a surface that rolls over at the higher elevation of 3720’. A third surface which enters this same immediate area from the E, coming from Little Owyhee Butte across the present course of the Owyhee River, seems to directly overlie the odd shaped lobe, and rolls over at a higher elevation of just lower than 3700’, and is separated from it by thin, light colored sediments.

So what do we have here? I think the odd shaped lobe is stratigraphically oldest, probably the Little Owyhee Butte lavas from the E are next, and that the E-facing scarp and surface to the W is the youngest. There is an odd meander in the course of the Owyhee in Sect. 32, T30S, R41E, rather square in map view, that is created by the eastward continuation of the lava flows of the odd shaped lobe, passing underneath the Little Owyhee River lava flows. I have a paleomagnetic site, in what I thought was Little Owyhee Butte lava flowsjust N of this area, that doesn’t fit so well with the other sites. I now wonder that it samples not Little Owyhee Butte, but the lava flows which come into the area from the W at the highest level. More sites on both sides of the Owyhee River will help decide this. Although surface degradation is the general process of this area through the last 4 Ma, these 3 units stack during a period of aggradation. I wonder how long it lasted? The NE projection of the oldest odd shaped lobe, and the W projection of the Little Owyhee Butte lava flows I believe is telling us about the location of the junction between Crooked Creek and the Owyhee River at the time of these eruptions. Not really that far from the current junction, located just to the SE.

Lastly, another curiosity for investigation to the south. In the area just N and E of where Crooked Creek crosses Hwy 95, the creek flows in a fairly sharp canyon for about 3 miles. The E and W rims of the canyon are at very comparable elevations, and we know that Bill Hart sampled the W rim from basalt flow outcrops for his argon age experiment. So I guess the E rim will probably be basalt lava flow outcrop too. But, that dark surface and dark layer passes laterally to the E all the way to the Cliffs of Rome, where I believe Caitlin showed me the odd erosional sediment columns of that area. I half remember the dark layer, but I remember it as a coarse fragmental layer, and not as any kind of lava flow. Can we see the transition of one of these basalt flows becoming deltaic, then fragmental, proceeding to a cemented black basaltic sand layer pro-delta? Is the transition from flow to fragmental about where a N-S canyon has be cut through the layer just SSE from Crooked Creek Ranch? The Rome 7.5’ quad shows quarries in this layer. What are they quarrying? Broken basaltic fragments just the perfect size for road metal? I can’t wait for the roads to dry out!

Area East of Saddle Butte

The air photos have clarified my thinking about “young” vents E and N of Saddle Butte. I believe the W-E “breadloaf”of lava located just S of Wrangle Butte is in fact a badly eroded isthmus between a lava flow field from vent 4373’ in the extreme NE corner of the Saddle Butte 7.5’ quad, and a S-sloping lava flow field bounded by Bull Creek Canyon, the Owyhee River, and a S-facing scarp located just N of Ryegrass Creek. Some field inspection S of Wrangle Butte near Top Hat Reservoir is required. The S margin of the flow field from vent 4373’W of this constriction is either Bull Creek, or a parallel drainage just to its south. Near Ryegrass Creek the lowest scarp from this flow rolls over at about 3780’ which is low, but not as low as other “young” scarps. Therefore, rather young, but perhaps not as young as 2 Ma. This lava flow field looms over Chalk Basin, and projects eastward forming the Basin’s S boundary in the Lambert Rocks 7.5’ quad. The last basalt flow outcrops appear again at about 3780’ in this area, but E and forward of those outcrops are broad, smooth patches of strongly oxidized sediment(?) that I wonder are palagonitized fragmental basalt and basalt sand. Is this another place where we can inspect the transition from subaerial basalt flow to lake sediments?

The photos have helped me decide that there is a basalt shield at the E base of Saddle Butte, with a vent at 4302’, that forms a lava flow field to the E and S, which rims the prominent SE-facing scarp that dominates the Wrangle Butte 7.5’ quad. This scarp breaks over at 4120’, is thus rather high and probably not all that “young”. As if I actually know what that means! The N end of this scarp is at Chanis Rock, which is the last place to actually see the rim basalt flow clearly. The N boundary of this flow field extends W from Chanis Rock, and is an important part of my reasoning that these flows come from vent 4302’, and not from Saddle Butte itself. There is thus a fat septum between this flow field, and the one described in the previous paragraph composed of rolling topography sloping E off Saddle Butte. This must be even older ground.

Lastly, the photos helped me note that S of Ryegrass Creek, in and amongst the terminating lobes of the 144 ka Saddle Butte lava field, is a low E-facing scarp. The 144 ka flow dump over this scarp, and mask it to some extent, but it extends all the way to the Owyhee River, and forms the walls of the unnamed canyon which contains Sand Spring, and a minor lobe of the 144 ka flows. Anyway,,,, off to the SW I lost view of a NE directed lobe of lava from the 4257’ vent in the Palomino Lake 7.5’ quad, because it was covered by the lava flow field of the 144 ka event. Is this scarp the terminus of the older flow lobe? This scarp rolls over at about 3700’, or perhaps a little lower. The lower elevation outcrops are softer, rounder, and subdued, making me wonder that again we can witness the transition from sharp, blocky subaerial basalt flow, to lava delta, to fragmental layer, to glassy, basalt sand fringe. Easy to get there and take a look. Other scarps associated with vent 4257’ lava lobes, roll over at elevation quite a bit higher than 3800’, so perhaps it is incorrect to associate these lower elevation scarps with that vent. Start the drill! Let’s see what correlates.

Sacramento Butte 

High ground 2 mi east of Sacramento Butte, that I am calling vent 4411’, seems to be the source of basalt flows with high elevation margins. Consequently, it may be rather old. Lava flows from it embay Sacramento Butte from the E, and pass both S and N of Sacramento Butte flowing W. An easily identifiable lobe is directly S of Sacramento Butte in the SE corner of the Sacramento Butte 7.5’ quad, and ends at a scarp rolling over at 4220’. Lower and Upper Clark Reservoirs are in the drainage that separates this lobe from Sacramento Butte. The vent 4411’ lava flows loom over, and form the W rim of Sand Basin and are found at variable elevations near 4300’. This scarp is erosional, and has to have retreated westward at least to some extent. Again, these flows are way up in the air, and may be 4 Ma old. The square shaped high mesa that looms over Rinehart Ranch on the W, may be a continuation of this flow field. My one-time belief that that mesa is just some “old stuff” up in the air is now gone. We will sample the square mesa, and tie it to one of these pre-Bogus rim flows.

So what to make of Sacramento Butte itself? Topography associated with it dominate about 6 sections that slope SW and end at Clark Ranch. A subsidiary knob at 4341’, on Sacramento Butte’s N flank, may be another different basalt vent. If that is the case then the Butte is even smaller aerially! This combined with George Walker’s Oregon state map data that Sacramento Butte is actually not a basalt, but somewhat evolved, makes me wonder that it is an old, masked volcanic center, and not anything of interest to our post-4 Ma geomorphic concerns.

The “Gooseneck” of Jordan Creek

It looks on the air photos that the lava flows from Owyhee Butte loop SE and behind Little Owyhee Butte, and may well make it all the way to the N side of Jordan Creek canyon, to the SW of Hidden Valley. When Kevin and I took the 3 paleomagnetic sites in the area, we just missed stumbling into this awareness, by only a couple hundred meters in one case. So we will go back and put a site into these flows and see what’s what. An odd flat bench, on the SE side of Jordan Creek, may be a continuation of these Owyhee Butte lava flows. They collectively have a SW slope, which does not make much sense for Little Owyhee Butte, but may for Owyhee Butte. An alternative possibility is that these are older flows, related to the NW sloping topography on the SE side of the creek. Doesn’t look hard to get there.

Diamond Butte area – Downstream from Birch Creek pullout 

I note something on the photos of this area, which I’m sure Kyle probably already knows. He knows everything first! [check these lavas out in one of my (Kyle) gigapans:] About a mile and a half downstream from the meadow at Birch Creek Ranch at which we pull out, are some very interesting outcrops on the E side of the Owyhee River. They are best expressed in the W half of Sect. 5, T27S, R43E. They are a doublet of basalt ledges, the upper one of which extends N almost 3 miles. One of them has to be Bogus Rim, but who is the other one? Better still, farther N on the extension of the upper ledge in Sect. 28, T26S, R43E is a knob with spot elevation of 3235’ that looks HIGHER than the upper ledge in the photos. Could we have three (3) ledges here?

I think we can walk to these outcrops, but it may not be easy. There are two reaches of the Owyhee River that are cliffs plunging right into the water. A jeep trail would get us part way N, but we will have to walk. We can pick up the water late, only at the end of the walk, and carry it uphill to the ledges. Paleomagnetic work here, combined with magnetic work on the ledges W and directly above Birch Creek Ranch, should make quite a package.

vent 4569’ – SE Deer Butte Rim – backside of Bogus Bench 

This vent was featured to some extent in Bondre’s recent dissertation. It is in the NE corner of the Bogus Bench 7.5’ map. You can drive right past this vent on the way to Greeley Bar vent and hardly notice it on the ground. But, it has a wonderful, and I think youthful, expression in the 7.5’ topography, breached to the W. No basalt lava flow field to any easy witness, just the cone. The Miami University folks (I don’t remember who now) have a 40/39 age on this at about 5.5 Ma. My guts say no way! I believe that I have UTM coordinates where the sample comes from. I believe that I have loosely played with those coordinates, and that the sample site is W of the cone (which appears in photos to have NO outcrops) from the rim area to its W. If this is true, then the dating sample comes from a potentially scary place. The rim there is a continuation of the rim S of Deer Butte, and looms above Mud Creek at its SW base. Recent age dating puts Deer Butte at about 4 Ma, not 5.5 Ma. Possible that the age experiments are a bit screwed up. But it is also possible that the 5.5 Ma age sample comes from a lower ledge W of the 4569’ cone. S of the 4569’ cone the rim is the lower flow, N of the cone the rim is the Deer Butte flow field. Shannon and I sampled that rim very near Deer Butte Reservoir #2. I will plot the age sample location and see what I see. The lesson here: NEVER let your petrologist collect your stratigraphic and age samples! KEEP THEM IN THE LABORATORY generating data on 40 elements to two decimal places of precision. We will visit this cone this summer(?) and try to sample it. Inspection of the air photos does not lead to optimism.

SW corner of Bogus Bench Mesa 

Cooper has called attention to an odd “cascade” appearance to the SW corner of Bogus Bench Mesa. It looks like the Bogus Rim lavas(?) have dumped down over and subdued the sharpness of the rim there. The source of these flows would be knob 4432’, perched right above the edge. But that ridge really is a continuation of vent 4487’ a half mile to the NE. In my “mapping” of Bogus Bench, I separated vent 4487’ from the rest of the rumply relief which seems to be the vent area for the Bogus Rim lava flows. Those vents/flows seem to embay vent 4487’, and are thus younger. At the foot of Bogus Bench is a bench of lava flows that, with a equal grade mirror bench to the S, pinches the Bogus Creek drainage near Bogus Lake. One could entertain the idea that the cascade down from vent 4487(?) makes these benches, which roll over at about 4100’. This places then 150’ higher than the Bogus Rim outcrop that Cooper and I sampled in 2006 at Bogus Falls. OK, higher bench,, older flows,,, vent 4487’,,,, older than Bogus Rim vent!!!!!

ONLY PROBLEM is that the bench S of Bogus Lake is a continuation of topography extending 3 miles E that has been buried by Clarks Butte, Forgotten Butte, and finally West Crater lava flows. The bench really appears to have come from the E, and thus can’t have arisen from any cascade over the SW rim of Bogus Bench. If it comes from the E, it might come from the relatively young Threemile Hill vent, or possibly from the “other” Saddle Butte. I suppose the Arock summit vent is also a choice, by a somewhat convoluted flow path. I also suppose they could correlate to the Bogus Point lava flow, but their higher elevation here would have to be explained away, by a dramatic slope to the W of the topography of that time.

Older topography in this area scares me a bit, as we know that significant down to the N faulting occurs just to our S from this area. Is the old topography in place, or foundered in big blocks to some extent? Tough to know. The air photos give no hint that the bench closest to the SW corner of Bogus Bench is part of the stratigraphy UNDER that bench. I think it is perched against that rim from the S, and thus substantially younger.

I have lost track of the full count of all the possibilities up to this point. TOO MANY CHOICES. What I plan to do is sample the N bench at the Bogus Creek pinch point, and sample the the S bench of the pinch point where the road S to Arock summit crosses the younger, overlapping lava flows. A quarter mile walk W puts me on that topography. We’ll see if they seem to be the same, and what they might compare to. Then, we need to get up on the extreme SW corner of Bogus Bench to take a couple of sites. I am hoping that the road to Bogus Bench Reservoir has been extended since the 7.5’ map was put together in 1972, and that we will only have a short walk. Spot elevation 4371’ looks to me to be a place where we can sample the Bogus Bench which is older, and NOT Bogus Rim lava flows. Just across the ephemeral creek to the N is the foot of the topography from vent 4487’, and maybe we can find an outcrop there. If not, there seems to be a S-facing ledge just W of vent 4487’ that looks like a possibility. So many plans!!
Arock shield – Bogus Point lava field

I have looked hard at both sets of air photos, and for the life of me I can’t see how the Arock summit shield merges with the underlying Bogus Point lava flows. There are a couple of linear gashes to the E of Bogus Creek well, which offer the chance of getting into the flows. But, they seem to be continuations of the W to E faulting that crosses the NW flank of Owyhee Butte, and may be inappropriate places to sample. Kevin and I drove the entire W flank of the Arock shield, and while we saw piles of rocks, we did not have outcrops jumping in front of the truck. We will snoop around, but do not have any concrete plan of action at this point. 

Friday, April 16, 2010

Now with lava!

This reach of the river (looking downstream, btw) provides THE perspective on the role of lava flows in displacing the river and instigating massive slope failure.

Posted via email from Fresh Geologic Froth

Very cool landslide visualizations: Owyhee River, Oregon

Using Google Earth pro, a tiled slopeshade map from LiDAR, and an exported and slightly generalized shapefile from my geologic map.

That's right...I chose mint green.

Posted via email from Fresh Geologic Froth

This one is making the rounds in the geoblogosphere...for good reason.

Thursday, April 15, 2010


This unadorned image of the middle Owyhee provides a nice backdrop to recent discussions that illuminate just how many volcanic vents are within our collective field area. This rendition is the slopeshaded 10-m DEM with a stretched color ramp overlay. This one is worth a long look. Note the topographic evidence for lava dams where we know they are, and then ponder where they also may have been. I hope to field check these for pillow complexes early this summer.

Saturday, April 10, 2010

Nearing the end...The Owyhee Map

I have spent many hours (while on family medical leave, no less) doing
the penultimate pass through the Owyhee map. Not only through the
detailed section but also out into the larger region from which the
lava flows originated.

Theses aren't the most beautiful snippets, but after one more pass,
the map will be nearly ready for external review. There is a chance
that Duane, Cooper, and I will do some additional fine-tuning of some
of the 'other' lava flows out know, the ones we have
largely ignored, but are hugely important in the evolution of the
Owyhee system.

Posted via email from Fresh Geologic Froth

Thursday, April 8, 2010

Interesting Ramblings from Duane (with maps from Kyle)

Young Basalt Fields in and near the Rome Basin

              A continuation of the Owyhee River Project, into a somewhat older time domain, offers an opportunity to use the same mix of riverene hydrology, geologic mapping, sedimentology and slope stability, volcanic geology, chronology, and lastly paleomagnetism studies, that were used in a rather younger timeframe.  Understanding of the evolution of the Owyhee River system from some network draining a Miocene volcanic upland toward a large freshwater lake in SW Idaho, to an entrenched stream following the Snake River toward the Columbia would be the target we would be after.  Lava flows and landsliding, perhaps at an initial “monumental” scale could have impounded lakes along the course of the Owyhee River that might have persisted for some time.  I am interested in this work just to figure out the number of separate volcanic events that may be involved.  Their separate directions of magnetization are of use to me.  Hopefully, you will also find reason(s) to wish to pursue this work.

              I have Kyle’s air photos now, and am looking into various “situations” I describe below.  I will have additional comments within a couple of weeks to add to those below.  So get your 7.5’ maps out, and follow along with my thoughts.

I will discuss these “young” lava fields, as they seem to group/align spatially (and probably temporally as well!) from the NW toward the SE. 

NW of Saddle Mountain

              There is a SW to NE alignment of young basalt shield volcanoes, to the W and N of Saddle Butte that morphologically seem quite young.  The pressure ridges and original topography of the flow field are still evident, and remind me of the general appearance of the Greeley Bar flow field.  There are 4 different vents named (in the absence of any real geography) vent  4528’, vent 4556’, vent 4521’, and vent 4373’.  They appear in the SE corner of the Turnbull Peak quad, across the Saddle Butte quad, the S half of Mustang Butte quad, and the SW quarter of the Sacramento Butte quad.  Their lava flows collectively move S and E to form the N margin of the 144 ka Saddle Butte lava field, embay Saddle Butte proper, and flow off to the NW and NE making the SE margin of “Barren Valley”.  I believe they embay an older Mustang Butte, but I need to look at the air photos to be sure.  Brennan Jordan argon dated one of these flows along the road to Rinehart Ranch, before you even get as far in as Crowley.  He obtained an age of 1.40 ± 0.04 Ma from BGC.  Pretty damn young!

Why should you care? – How these flows “finish” to the E is not clear to me.  They may have interacted with “lake(s)”of the Owyhee River in the Wrangle Butte quad area.  One flow tries to sneak S of Saddle Butte, but seems be be pinched off by Saddle Butte topography W of Rattlesnake Cave.
Another flow clearly is moving SE past the SW of Wrangle Butte, but what happens to it in the Bull Creek drainage is again unclear.  The topography between Wrangle Butte and Chanis Rock also seems odd.  It is kind of an E facing scarp, and a continuation of the more pronounced E facing scarp to the E of Saddle Butte.  I wonder that an W-E “bread loaf” of topography between Top Hat Reservoir and Bull Creek is an eastward continuation of these “young” lava flows.  Farther E a platform of flows, now S of Bull Creek canyon, form the W and SW margin of Chalk Basin.  This platform is asymmetric across Bull Creek canyon, with the S bank breaking over at about 3940’, and the N bank breaking over rather higher at 4060’.  Is the end of the “younger” flows pinned to a lower(younger) base level?  The platform slopes to the S another 4 miles, ending in a S-facing scarp just N of Ryegrass Creek.  There these lava flows are asymmetric across Ryegrass Creek, with the 144ka Saddle Butte lava flows on the lower S side.  These flows also shoal against a SW-NE ridge of older topography located just N of Ryegrass Creek, and just W opposite Lambert Rocks. 
Lastly, the topography just SE of Saddle Butte catches my eye.  Are these Saddle Butte flows forming the prominent SE-facing scarp N of the Saddle Butte lava field?  Or, is there a younger shield, broadly centered in the SW corner of Sect. 17, T29S, R40E.  I hope the air photos will help me decide, because in Google or Bing satellite images it is not clear.  I believe that Saddle Butte is composed of somewhat evolved lava flows and not actually basaltic.  Perhaps we can tell just from hand specimen where these flows come from.

Sacramento Butte

              The topography of this butte also catches my eye.  It forms a prominent W-facing scarp, framing the E side of the Barren Valley.  We drive partly over its surface on the way to Rinehart Ranch.  It did not strike me as particularly young, but it did not seem as old as Deer Butte either.  While its source vent is clear, the topography N and E of that vent suggests either significant erosion, or that another unnamed vent area is 2 miles ENE of the vent.  Are these “two” vents allied in time?  That “vent” forms scarps with breakovers at and above 4300’.  While high, this is still lower in elevation than Deer Butte, which is only 4Ma old.  Is this vent younger?  Sacramento Butte’s W-facing scarp breaks over about 4160’; does this mean it’s younger, or was this just the sort of relief on the “upland” surface?  I am curious about these volcanoes.  They are probably older, but perhaps by not that much.

W of Iron Mountain

              Several shield volcanoes in the vicinity of Iron Mountain may be rather young.  Farthest W is vent 4838’ which is located at the W side of the kipuka within the 144 ka Saddle Butte lava flows that we cross on Hwy 78.  Bill Hart may have an argon experiment on these lava flows.  These flows move SE and end in the area of Palomino Lake.  The relief of this flow field surface strikes me as rather young.
              Another vent, called vent 4257’ in the SE corner of the Palomino Lake quad, is perhaps a major source of “young” lava flows.  It passes N of Iron Mountain, and bifurcates into two E directed arms around some old topography.  The northern arm seems to end on a broad E slope to the S of a minor flow projecting E out of the Saddle Butte lava field.  The southern arm continues E well past Iron Mountain, into the Owyhee Butte quad where I fear it hides under thin sediments, possibly all the way to the present course of the river.  This southern arm has N-facing and E-facing scarps that break over at about 3840’ that both seem to die out as they pass into the Owyhee Butte quad.  Again, are they masked by sediments, or do the flows pinch out?
              Another arm of flows from vent 4257’ passes W and S of Iron Mountain, with Palomino Creek probably forming its SW margin, going all the way to Burns Junction.  This arm bifurcates around Scott Butte, passing eastward between Scott Butte and Iron Mountain, ending at an E-facing scarp the breaks over at about 3840’.  Isn’t that interesting?  SE of Burns Junction, the flows go some distance down Drought Creek, and pass E past Burns Junction, probably ending in some odd topography where Palomino Creek dumps over a broad E-facing scarp.  Some maps put a N-S fault through this topography.  In any case, vent 4257’ is a bit of a brute.
              Iron Mountain itself, may be a relatively young basalt shield, though it seems clearly stratigraphically older than the vent 4257’ lava flows.  Lava flows from the vent move SE, and end at an E-facing scarp that breaks over at the same elevation as the vent 4257’ lava flows N and S of it have.  Can you say “Graded to the same level?”  Perhaps Iron Mountain and vent 4257’ are part of a single time episode, with two vents; first Iron Mountain, then vent 4257’.
              A vent called “Dome”, in the Palomino Lake quad, which is almost nested within the Saddle Butte lava field, may or may not be a young vent.  It probably bears some inspection on the ground, and at least a single paleomagnetic site.  Hart also believes that Scott Butte is about 1Ma in age.  Morphologically, I can believe this, but I want to see the air photos, and eyeball it from the ground also.
              In the Rome quad, Bill Hart has generated two K-Ar ages on flows on the W bank of Crooked Creek.  I thought these were within the State Wayside Park, but they are actually several miles N of there.  He found an age of 0.91 ± 0.36 Ma on the “rim HAOT” and an age of 1.25 ± 0.28 Ma on the “lowest exposed flow” about 30m lower in elevation.  Although both these experiments need to be replaced with 40/39 work, these experiments say these scarps are 1-2 Ma in age, and NOT 3-4 Ma in age.  The upper date seems to be in flows from vent 4257’.  Lower age is less clear.  Some topography, E of Scott Butte, may be a local basaltic vent.  It seems to be embayed by the vent 4257’ lava flows, but could be the source of the lower ledge.  DRILL THEM ALL!  And let God sort them out!

Why should you care? – We evidently have at least two young flow fields moving eastward and ending in E-facing scarps, possibly interacting with the Owyhee River.  We should frame them stratigraphically, get better ages, and look at the stratigraphy they hold down and hold up.  Might they have a pillowed margin, or some fragmental character?  “Young” very clearly comes from the W and gets to, or gets near the Owyhee River.

S of Hwy 95

              There are a couple of basalt lava fields to the S of Hwy 95 that catch my eye, but the flows from Jackies Butte, may be the only lavas that have interacted with “lakes” in the Rome basin.  A smaller, and probably older vent, SE of Burns Junction may also be of interest.  These flows are just E of Anderson Reservoir, so I call them the Anderson Reservoir vent.  Crooked Creek is W of these flows, Rattlesnake Creek is E of them, and Drought Creek flows SSE before joining Crooked Creek and flowing NE through a funny little canyon cut across older terrain.  George Walker mapped the young flows from vent 4257’ as flowing SE, down Drought Creek almost to its join with Crooked Creek.  I am going to check if this is correct.  Perhaps the vent 4257’ flows are the reason that Drought Creek turns abruptly S, from a former course to the NE, perhaps joining Palomino Creek S of Scott Butte. 
              The Anderson Reservoir flows seem heavily mantled by sediments, possibly suggesting greater age.  And, no “vent” construct is easily visable either.  But, I recall that Crooked Creek has glacial breakout floods from the Steens country, and perhaps they have carried enough sediment to prematurely age these flows.  The eastern scarp of this flow field, where it can be seen, breaks over at about 3840’, and perhaps that means something to us.
              The Jackies Butte flows have been K-Ar dated by Bill Hart at 0.36 ± 0.13 Ma at a site farther SE along Rattlesnake Creek.  The age strikes me as a tad young, but again, it is not a 3 or 4 Ma flow field.  If it is this young it should have normal polarity.  Jackies Butte lava flows form a prominent N-facing scarp at the S end of the Rome basin.  It breaks over at about 3890’, but may be relatively thin flow on a more than 100’ scarp mostly in sediments.  We should inspect this margin to look for evidences of water-lava interaction.  The scarp ends to the E in the vicinity of Rockhouse Reservoir.
              Lastly, the basalt shield of Water Hole Butte may be of interest.  It may be as old as Deer Butte, or even older.  It backs SE onto even older topography, and abuts Jackies Butte over a more than 6 mile saddle between them.  Its western flank is faulted rather severely which may be telling us something about its age.  One of the fault traces cuts across the contact with Jackies Butte and breaks those lavas too.  It is unlikely that this flow field interacts with the Owyhee River, and it may be one of the “upland” basalt volcanoes that preceed the downcutting witnessed over the past 4 Ma. 

Why should you care? – I think clearly that Jackies Butte, and possibly the Anderson Reservoir vent have something to tell us about Owyhee downcutting and how Crooked Creek has adjusted to that arena.  One of Kyle’s shoreline maps laps against the N scarp of Jackies Butte. 

SE of Rome

              A young flow field, on the E side of the Owyhee River may also help us understand the River’s history.  The surface of the rim behind where we put into the Owyhee River is covered by flows from Round Mountain, which is about 5 miles off to the SE.  Bill Hart has a K-Ar age of 1.49 ± 0.18 Ma on an outcrop of this lava flow field.  This age needs to be replaced, but again these flows are no older than 2 Ma, from the age work in hand.  These flows shoal northward against some older terrain (4 Ma (?)), that I think I sampled at the top of the grade before you drop down to the Owyhee bridge on Hwy 95.  They also infill block-faulted terrain to the SE, having an edge that is difficult to pick up from Google or Bing.  The elevation of the W rim of this flow field does not seem very constant.  It is as low as 3700’ above the put-in, and climbs southeastward to almost 3900’ up river.  It evidently is mantling sloping topography, and doesn’t seem to be “lake bound” in any easy way. 

Why should you care? – The edge of this young flow field determines the course of the Owyhee River over a distance of 8 to 9 miles.  Parts of this flow field are on the SW side of the river, meaning that this flow might have filled and buried the former canyon of the Owyhee River.  Should we be looking for a filled channel in the eastern wall of the Owyhee S of the put-in park?  Will we find evidences of lava-water interactions along its western margin?  We should investigate this young flow.

Wednesday, April 7, 2010

You want lava, landslides, inverted topography, lava-water interaction, and more?

Maybe a trip to this part of southern Argentina is in order. Check this out:

Visit this area here: