I hadn't considered wreckage. I remember finding a jettisoned fuel pod in a canyon once. Could be!
The reflection was surprisingly bright -- like a very smooth, glassy surface. In my experience, desert varnish tens to be somewhat irregular. Could be an exception, though... I did find some palm-sized sheets of transparent crystal in the wash, something I've seen before in Gower Gulch as well. Not quartz, more like calcite or -- wait a minute, Googling --
Gypsum. That's probably the palm-sized crystals. There's a place in Utah called "Glitter Mountain" that's all, well, glittery, from the gypsum crystals scattered on the surface.
Colemanite also forms crystals, and it's the main ore that was mined for boron in the Funeral Formation. I didn't find any images showing flat, tabular forms, though.
Meyerhofferite. Never heard of it. But there's a photo on http://webmineral.com/specimens/picshow ... JAVCXWYVUQ
, and the specimen is identified as coming from 20 Mule Team canyon. Again, not really something that would form sheets, though.
I'm guessing crystalline gypsum. I may have a try at getting closer when Laura and I are down in the Valley next week.