mdog,
I have found a few items that have helped me date sites, but only within 50 years or so. I once came upon a hole near a water trap that I first believed was a site for a shrine. After digging out a couple hundred years of dirt, dust, and roots, I uncovered what I believed was 3 chisels. A few years later, I met a gentleman at the Quartzsite Gem and Mineral show that was a professor at an, (unamed for his protection), university here in the west. I let him take one to study, and I believed that would be the last I heard from him. Almost 2 years later, he called and told me they were wrought handmade iron ship nails, that had been converted to chisels. Even though he dated them to the 1600's, I believe that was for thier original purpose. Much later on, I believe someone happened upon them and brought them north to use for mining / caching purposes.
I have also found square, handmade nails, a covered hole with 16 mule shoes in it, 2 broken mule bits, and on. I have never had the latter dated, but have seen photos that are of the same bits, that are declared to be late 1700's to early 1800's.
The strangest find I have ever made was a pile of 12 ancient Chinese bronze coins, from what I believe was the Quing Dynasty. Tons of these were made, but how they found there way to the middle of nowhere on a mountain in central Nevada, I have no clue. Must be a story there...
I could go on forever about the "clues" I have found, but better give it a rest.
Bytheway....this has been one heckuva hot summer! What I usually can accomplish in a week in the hills, has been taking two....(no way it could be my age creeping up on me)...
Is the Colorado River navigable from southern Nevada down to the gulf? Also, is there enough timber, along the Colorado to make flatboats? I was thinking about those nails. Along the Mississippi River, during the 1700s and 1800s, traders would make flatboats and float their goods to one of the port towns, sell their boats for the timber, then walk home.