Woops, Texas Camper is right, the play is in Palo Duro Canyon State Park, not Caprock as I incorrectly stated. But, Palo Duro is the one near Amarillo.
And yes, "Texas" is an outdoor drama that is put on in an amphitheater in the park. Here are some links with info about the park and the drama.
http://www.palodurocanyon.com/
http://www.tpwd.state.tx.us/spdest/f...rks/palo_duro/