I can't stress more strongly that someone like GeoMitch, who has not only done graduate work in the area but has probably worked the section professionally since his training, is the true resource in matters such as this, not yours truly. I feel absolutely inadequate to do anything other than SWAG when it comes to a setting as historically and presently as dynamic as Death Valley. But what the heck, it ain't like I'm preaching "settled science" for political gain, so here goes:
From all of < 30 minutes skimming of some USGS pubs from the 1960s and a couple of other more recent sources, the pluton/batholith sized granitic intrusions generally mapped as either the Paiute Monument or the Pat Keyes intrusive are huge in aerial extent and fairly old by DV standards--mid- to late Mesozoic (mid Jurassic to late Cretaceous). With the extraordinary degree of horst and graben development from the late Cretaceous through last week, it seems that with source rock areas the size of batholiths (generally 40 square miles or more in aerial extent), we might expect extensive near-surface spheroidal weathering within the outcrop area of the plutons and mass wasting to combine to form widespread interlocking alluvial fans containing extensive granite cobble and boulder content which could cover many square miles of area away from and off of the flank of the batholiths, over then-recent basalt flows forming mainly in the valleys,, only to be covered by younger basalt flows. If we were to envision the exact area photographed as having been near the toe of alluvial fans, we'd expect some mix of smaller boulders and cobbles and finer fan sediments, including clays. We'll remember that the extensive feldspars within the granites to also chemically weather into clay minerals, also, such that the toe of the fan could represent a more gently sloped area on which a paleosol might develop. Then, turn on the faucet of more basaltic flows from a nearby vent, and the relatively thin veneer of "toe of the fan" deposits are sandwiched and somewhat protected from erosion by the basalt "cap" and thus preserved until Andy and Ms. Lighthawk arrive on the scene with a great deal of curiosity and expertise with the camera.
The USGS pubs mention outcrops of the Paiute Monument and Pat Keyes plutons including boulders up to 50' wide partially buried in a soup of quartz and feldspar sand, so perhaps that development within an alluvial fan deposit miles away from the main outcrop area continues after the initial transport from the outcrop area of the granites into the deposits of the fan and have the look and feel of a quartzite interfingered with clayey material which had been either actual sedimentary clays or weathered feldspars.
One thing I have the hardest time envisioning is the extensive very young and ongoing uplift and down-drop (horsts and grabens) of the present day DV area ranges and valleys, and to a great degree, all over the Mountain West I'm much more wired to expect little to no Cenozoic tectonic activity (though much to the surprise of many, some very recent detailed geologic mapping in the Blue Ridge Mountains has led to the inference of Neogene uplift in the form of vertical faults with movement the order of tens to > 100 meters right in the heart of the Southern Appalachians in Boone, NC). So much for "settled science", eh?
Anyway, what you found and photographed is absolutely fascinating to this old geologist, and I hope to learn more about it in the future, especially when some geologists with a far better understanding of the area than I have can weigh in on the matter.
Foy