Just what causes those rockslides?

I've never liked driving through a narrow canyon during a rain storm or when the snow is melting a lot for fear of rock slides. They happen frequently around here including one that closed I-70 during Thanksgiving vacation one year and we ended up with an extended stay because of the serious damage to the road. But we've never been up close and personal to a slide -- until today.

We decided this would be a great morning to bike to Hanging Lake, a ride of about 12 or 13 miles along the Colorado River. We were doing fine, enjoying the gorgeous scenery until about 4 miles into the trip.

Tom stopped to move a boulder off the path:


While stopped here we began to hear rocks sliding down the slope to our left. What a surprise. It was a bit nerve-wracking but really neat, too. Remember, I'm not a pro so the video is somewhat wonky:



Once we got up to Hanging Lake we came upon a group of lovely Amish women who had just biked in. Can you imagine riding a bike wearing a long dress? Didn't seem to bother these ladies.