Map Area in Meadow Valley Wash

We - MOH and I - recently returned from a trip that took us to points south. It was kind of a quick trip, but we did manage to drive by the first area I ever mapped professionally, back in the uranium exploration days of the late 1970's.

This first map area is in Meadow Valley Wash, about 19 km (12 miles) south of Caliente, Nevada, just north of the Boyd railroad siding (general location map). Meadow Valley Wash is a river most of its 177 km or 110 miles (length according to Wikipedia), especially south from Panaca. I saw intermittent stream symbols on the map only intermittently (ha!) in the area northeast of Panaca. It's headwaters are in the White Rock Mountains and Wilson Creek Range on the Nevada-Utah border northeast of Panaca. From Panaca it then flows mostly southward towards the Colorado River, via the Muddy River, which it enters near Moapa, Nevada. The Muddy River flows into northern Lake Mead.

Meadow Valley Wash is prone to flooding. One recent big flood was in 2005. The shapes of things have changed since the last time I was in the area 31 years ago. The river channel has moved around some in the Rainbow Canyon area between Caliente and Elgin; some old roads or river crossings appear to be gone.

And now I've gotten away from the main point of this post, which was my first professional mapping experience. We were in the area to look for uranium in the Tertiary volcanic rocks in the area of the Caliente caldera complex, and also in and near the younger Kane Springs Wash caldera to the south and southwest.

The altered and strongly hematite-goethite±jarosite-stained zone - that mass of light orange to red-orange to red-brown rocks in the photo above - is part of a rhyolite flow, dome, and dike complex probably associated with the formation of the Caliente caldera. The altered rhyolitic rocks - which overlie altered older andesite flows and flow breccias, and underlie mostly unaltered younger ash-flow tuff units in the map area - gave a strong radiometric anomaly, which ultimately proved to be due to high thorium (and at least normally high potassium) rather than from high uranium. We thoroughly mapped and sampled the area of interest and took a lot of ground scintillometer readings. Our scintillometers read in α (alpha), β (beta), γ (gamma), and Total Counts, and looked something like the scintillometer in this picture.

Continued at Our Camp in Meadow Valley Wash.


Some References:
Harding, A.E., Scott, R.B., Mehnert, H.H., and Snee, L.W., 1995, Evidence of the Kane Springs Wash Caldera in the Meadow Valley Mountains, Southeastern Nevada: in Scott, R.B. and Swadley, WC, eds., Geologic Studies in the Basin and Range - Colorado Plateau transition in southeastern Nevada, southwestern Utah, and northwestern Arizona, 1992, U.S. Geological Survey Bulletin, 2056-E, p. 131-179.

Page, W.R., Dixon, G.L., Rowley, P.D., and Brickey, D.W., 2005, Geologic map of parts of the Colorado, White River, and Death Valley groundwater flow systems, Nevada, Utah, and Arizona: NBMG Map 150, map and text.

Rowley, P.D., Nealey, L.D., Unruh, D.M., Snee, L.W., Mehnert, H.H., Anderson, R.E., and Gromme, C.S., 1995, Stratigraphy of Miocene ash-flow tuffs in and near the Caliente caldera complex, southeastern Nevada and southwestern Utah: in Scott, R.B. and Swadley, WC, eds., Geologic Studies in the Basin and Range - Colorado Plateau transition in southeastern Nevada, southwestern Utah, and northwestern Arizona, 1992, U.S. Geological Survey Bulletin, 2056-B, p. 43-88.