The answer is:
They wore sandals!
That's right, prehistoric flip flops!

The earliest sandals found in Texas are more than 4,000 years old. Now how could sandals last so long? Were they made of steel? Of rock? No, they were made of plants!

Archeologists have found lots of sandals in the Chisos Mountains in the Big Bend area of Texas. Others have been found in the Rustler Hills and Franklin Mountains close to El Paso.

But how could these sandals have survived thousands of years in the wind and the rain?