Gopher snakes look something like a rattler and they are one of the most common snakes in the U.S. They have a faint diamondish pattern on the back and will mock the behavior of a rattlesnake including coiling, tail shaking and mock strikes. A lot of gopher snakes get killed for this sort of behavior. They have a smaller and non-triangular head and, of course, no rattles. They are also slimmer through the body and can get to be much longer than the western diamondback. Also, the western diamondback has alternating black and white stripes on its tail just forward of the rattles hence the nickname "coontail". The western diamondback is the most common rattlesnake in the western U.S. but is not the only western rattler. I have personally seen sidewinders, Mojave, Arizona black, and tiger rattlesnake; none of them have the distinctive "coontail" of the western diamondback.