Stepped out my back door yesterday to find this.
Those blocks are 12"X12" and cover the area where my septic tank is located. When I bought this place I had to pay someone to come out and tell me where it was so I would not build something on top. If fully stretched out it would be about 4 feet long. Since it was not a rattler I left it alone. Snakes help keep the rodent population down.

Last year I found a red racer in the front yard. Again non poisonous. But we do have the nasty ones, among them the Mojave Green that has a neuro toxin venom. Very bad, as well as the more common diamond back.

A rattler will have a wide, spade shaped head and of course he rattles on the tail.