Saw a salmon pink rattler slithering under a rock and sometimes saw individual scorpions scurrying about on a three-week trip to Arizona.
Living in New Mexico I was working at Ghost Ranch and on a harder run when I heard an awful hiss. I'd almost stepped on a mountain green rattlesnake which are supposed to be rare and also more temperamental. I also once put my foot down on a log to tie a shoe and about 60 baby scorpions came teeming out. Heart-stopping moments there.
Saw tons of rattlers when I lived in Colorado and also an occasional black bear. Once heard a mountain lion snarl -- unmistakable. Bald eagles, golden eagles, all sorts of birds. Elk sometimes, not sure if I'd want to count deer. Saw a woodpecker chipping away at a tree in the middle of a cold January run at Boulder Rez, saw a snow-white owl in a tree with bright orange (fall colors) leaves in north boulder, and saw a white-coated mountain goat too, which looked like a ram on Mt. Sanitas.
In Portland I saw a redtailed hawk on Wildwood on the ground, eating a grass snake of some kind. I was five feet away staring at it for several minutes and it just looked at me sideways and kept eating. A few coytoes too.
In Calif. I've seen bobcats, rattlers and coyotes oin the Bay Area + numerous bears in the mountains. Tons of birds, once saw a bald eagle in the Berkeley Hills and that is really rara as I am told there are less than a dozen recorded bald eagles in the central Bay Area (you see them all the time in Colorado, for example). Also saw a ring-tailed fox in Berkeley. You have to watch out for the raccoons in the Bay Area too, they are not that afraid of people.
I was coming down Shaver Grade above Ross Commons / Phoenix Lake on the north side of Mt. Tamalpais and I saw a mountain lion. It jogged by about fifty meters in front of me and didn't pay to much attention to what I was doing (A: shaking in my boots).
One of the oddest things I've seen was doing a run at Pt. Reyes. I'd finished at Drakes Beach which has cliffs you can sit on and watch the water about 75 feet below you. This sea otter was bobbing around. After about 20 minutes I saw a great white shark come along and snatch him right up for lunch. It was utterly ruthless.
Also saw a really pissed off baby cottonmouth (the worst venemous snake to encounter is a baby) in the South when I was out there for awhile. It sure would have been nice to have had a camera for some of those run ins.