I'm still shocked, horrified, dismayed, rattled, by how big and fat these creatures can become. I have no problems with bears; a four foot or longer fat rattler just freaks me out. Yes, I know they're all God's creatures…right up until they bite you.
I hike quite a bit around Mt. Diablo–apt!–and have never seen a rattler. What trail did you see it on, so I can avoid it (kidding). (I have seen a mountain lion there…).