GEORGETOWN ! ...
Thats practically the bulls eye of central Tx for the ancient peoples...in the search block above, type in NIGHT DIG. ( be sure to hit VIEW ENTIRE THREAD. ) The San Gabriel river was a major freeway.
Way farther south, running right through Round Rock is Brushy Creek....another very active area for the ancients.
You will certainly meet other creek surface hunters in the drainages after every rain / washout.
Even farther south is Walnut creek...Not only arrowhead possibilities but rich in fossils.. See front page bottom " OTHER FINDS"
All of Texas sits on fossils..Front page again, see SHARK TEETH TRIPS.
There's a fossil club in Austin that meets once a month then does field trips once a month. Palentoglogical Society of Austin.