Older Sediments Than Muddy Cr Formation

Looking at old sedimentary contacts with metamorphic Gneiss, pluton Quartz Monsonite, and lava Basalt. You can't directly date sediments so you find contacts with dated igneous rocks or sky fall ash.

Videod as dark desert pavement sediments:
Qoa Older alluvial deposits (Pleistocene)—Moderately to poorly sorted sand, silt, clay, and gravel. Poorly bedded to massive, weakly to moderately consolidated. Surface has slight to well-developed desert pavement and scattered to widespread pedogenic carbonate debris. Mapped on margins of Eldorado Valley.

Videod as red clay sediments:
Tsmo Older intermediate-age sedimentary rocks (middle Miocene)—Sandstone, mudstone, siltstone, limestone, gypsum, and conglomerate. Deposited in fault-controlled basins and subsequently faulted and folded. Locally includes megabreccia deposits and airfall tuff. Occurs on west side of Malpais Flattop Mesa, on east side of Eldorado Mountains west of Roaring Rapids, and east of Boulder City, where it contains conspicuous manganiferous gypsum in vicinity of Boulder Rifle and Pistol Club. Inferred to be about 12 to 16 Ma in age. At Malpais Flattop Mesa, unit lies between andesite lava and breccia of lower part of Patsy Mine Volcanics (Tpl) with an 40Ar/39Ar age of 15.72±0.03 Ma (Faulds and others, 1999) and a basalt flow of upper Mount Davis Volcanics (Tdmu) with an 40Ar/39Ar age of 12.73±0.3 Ma (Faulds and others, 1999). To west of river, includes basalt flow dated at 13.68±0.16 Ma (40Ar/39Ar; Gans and Bohrson, 1998). Unit is equivalent to sedimentary rocks of Mount Davis Volcanics (Tds). Maximum exposed thickness approximately 75 m

Geologic map:
https://pubs.usgs.gov/of/2013/1267/a/

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