Dryer
good rock was a extremely valuable commodity. Yosemite obsidian has been found in south american artifacts. Good spalls (flat and thin) could be packed up and carried away for trade. Anyplace with crummy rock traded for rock that could be used for tools. Those guys also spent a lot of time looking and alluvial deposits around streams was a good place to look.
Jim
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These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.