Leto Agtreides II said:
What time of day was this? At this time of year what time of the day are you most likely and least likely to see one of these guys on a trail like this? I'm assuming they're most likely to be out in the morning before it gets too hot so I've been terrified of this happening on morning trail runs.
**Not an expert**
This was before 10:00 AM. In my experience, you are most likely to see these guys before it gets too hot (early morning) or directly after a really good downpour. My general advice to people who like early morning trail running is to keep one eye on the trail and one eye looking for the glint of a spider web. Early morning contrast (particularly in the shade) makes it really difficult to spot everything, so there is definitely an inherent risk. Once the sun is high in the sky the spider webs burn off and the snakes seek cover. I can't imagine riding a mountain bike through tight, single-track trails. It would be virtually impossible to avoid a sunning, camouflaged snake.
Quick anecdote, I was trail running @ around 8:00 min/mile, navigated a tight turn bordered by tall brush and grass, and the largest western diamondback I've ever seen was on the trail. My split-second choice was to jump sideways into the brush (risking injury) or jump over the rattler. I chose the latter. Probably the most exciting (and terrifying) half-second of my life. Remember when you were riding bikes as a kid and took a nasty tumble? The feeling like the abyss was kind of staring back at you as time stood still? Felt like that.