I believe this to be a gopher snake. They pretend at being rattlesnakes, but conspicuously lack a rattle, though their mimicking ability of the posture of a coiled rattler is impressive. They are non venomous, but will bite and are occasionally aggressive. They can be identified by the row of large spots running down the center of their back flanked by a row of smaller spots offset from the center row, on either side.

ohio.edu/people/brune/calif-mar11/gopher_24mar11_2b.jpg