Crotalus

We killed this rattlesnake last night, at about one AM. He or she was hanging out underneath our house, near the stairs.

This one rattled right away, so we were able to bring the dogs inside before they even realized the snake was there.

This is a Western Diamondback, Crotalus atrox, which is probably the most common venomous snake here.

We had expected to find one at the coop, but this one preferred our stack of wall tiles and mastic.

I've zoomed into the head to show the ocular scales. I've talked to a lot of people about how to tell a Western Diamondback from the more dangerous Mojave.

The most definitive difference between the two is the number and size of the scales between the snake's eyes.

Many small scales between the eyes prove that this snake is a Western Diamondback.

Just a few large scales would indicate a Mojave.

This one also demonstrates an even pattern of white and black stripes on the "coon tail" section below the rattle.
Mojaves are more likely to have a predominantly white coon tail.

Many people will tell you that green rattlesnakes are Mojaves.  But color is actually an unreliable indicator, as both species appear in a wide (and overlapping) range of colors.

Black Tail Rattlesnakes are also often greenish-colored, but much mellower and they have a very distinctive black tail where the coon tail section would be.

But then (just when you thought you knew what you were looking for) there are wild hybrids.  Snakes that are both WD and Mojave.  If that's the case, then all bets are off.