White Crosses in So. NV

[Goat]

I've noticed some white crosses, laid out flat on the ground, during several desert excursions here in So. Nevada. They are approximately 1-2 feet wide, and 10-12 feet long. some of them are in rather inaccessible areas, and some are a few hundred feet from a dirt road. I've asked a friend (whose family owns the Techatticup mine) about them, and he suggested that they might be used for aerial photography (map markers?). I've also heard theories about helicopter landing areas (doesn't seem plausible in some places due to the rocky sloping ground), and markers for skydivers.
Some of the crosses are made of what appears to be nylon (held in place with rocks), some are a powdery substance like chalk, and others are formed from white rocks.
Does anyone have any ideas about the origin, or intended purpose of these crosses?
Thanks,
Goat

[Bob]

Your friend is correct. If you investigate, you'll find a USGS marker nearby. I say nearby because I think some of those markers were survey in bar on the Boulder Highway (They aren't set that accurate - 10s of meters off sometimes) and the Aerial survey people seem to locate them in the correct section points.

[Goat]

Thanks for scratching that brain-itch of mine, Bob! That's been bothering me for a few years now...