You are getting dangerously close to a juvenile western rattlesnake. Juvenile rattlers are the most dangerous of them all. When they bite, they inject more poison. Also, the poison is thought to be more concentrated.
I almost stuck my hand in this sneaky little guy's hiding place. I was climbing up a cliff last month in a remote part of eastern oregon, and just happened to see him in a nearly blind hand-hold. Luckily I had a cell-phone with a camera on it so I took his picture. You can't see from the photo, but he had only 2 baby rattles. They were vibrating like crazy, but they didn't make a sound.