We have the Western Rattlesnake in the Gold Country of Northern California where I hike and backpack. They call it the Gold Country because it's where the gold rush of 1849 started. The Western Rattlesnake is not an aggressive species normally, but once I rounded a trail and encountered a fully aroused Western Rattler coiled, raised up, rattling up a storm, and staring straight at me. It's amazing how loud they are. A jogger had just passed me going the other way and I reckon he must have stepped on it or agitated it in some way. I watched it for a few minutes and eventually it slithered off into a Poison Oak bush, still rattling, and settled down.
Another time I was farther up in the foothills and heard a commotion up ahead of me in some tall Manzanita bushes. Three ladies had encountered a big fat Western Rattlesnake sunning itself right in the middle of the trail. Being the chivalrous type, I nudged it off the trail with a stick, and it sluggishly crawled off to the side, never rattling once.
It is very rare to hear of someone being bitten by a rattlesnake here, and when it happens they usually survive. In fact I consider Mountain Lions to be a bigger threat, as a female jogger was killed and partially consumed by one near Cool California (yes there is a small town called Cool California) about 10 years ago. You can search for an account of it on the internet if you are interested. There is a memorial bench along side the trail in her honor. Personally, I like rattlesnakes, and like to see them on my trips, but I would prefer they not be in the middle of the trail.