you can't see the base, a green outdoor carpet platform (with sensors in it).. but this is one of the many aid stations on the range. The sign says (in both english and spanish):
Attention! You cannot walk to safter from this point! You are in danger of dying if you do not summon help! If you need help, push the red button, U.S. Border patrol will arrive in 1 hour. Do not leave this location.