You're not overwatering, especially in this heat. They probably need more this time of year unless you've got them in a huge mulched basin and/or real problems with drainage in your caliche. Even the tough drought tolerant natives can be surprisingly thirsty when getting established.

I would only be watering them once a week right now. The area of my garden that gets the most water is getting once a week. But water d-e-e-p. With watering too often, you open yourself up for humidity problems with plants that prefer dry air (unless you are drip watering). Your plant could be suffering from heat stress though?