(http://elliquiy.com/elluiki/images/a/a0/DFWgeology.jpg)<br/><br/>Seraph also mentioned rocks.  Here is a map of the strata underlying the DFW area.  Their camp is roughly located where the arrow shows "flood plain and terrace deposits".  In other words they've got a lot of dirt below them before they hit rock.  There are some rocky outcropings not far west of them but it will mostly be sandstone.  Which is crap for making tools out of.  Sandstone is so brittle you can crumble it with your hands.<br/><br/>Washita Group found farther west is "alternating thick clay units and thin limestone units; clay, calcar, commonly sandy, dk bluish gray and black; limestone in lower part hard, bluish gray to shtie, in upper part soft, thickbedded"<br/>