Several of these were patiently waiting for any of the abundant Mosquitofish, Gambusia affinis to pass below. Just after I mentioned this to my companion, one of the spiders made an attempt, but failed.
It was building a nest.
1st photo - with camera flash
2nd photo - without camera flash
This fellow survived an attack by a predator, probably a Coyote, as indicated by the tooth marks on the back quarter of the carapace, and the healed wound to the eye that faces the camera.