The group with aero bars may have been triathletes or cyclists training for a time trial. Aero bars are disallowed in events (like our local Tour de Tucson), but they are not illegal or anything.

I imagine 10 miles on a mountain bike would definitely be an accomplishment. I have only ridden one once, and we rode about 14 miles on pretty easy trails. I was definitely worn out!

I'd love to be able to ride 1-2 mph faster than I do, but I am happy to appreciate all of these things: I'm not struggling with any major physical obstacles and I was able to ride over 50 miles in the last two days and I enjoyed beautiful desert scenery, appreciated the monsoon season clouds and the greenery they have produced on the hills, watched a sunset and a sunrise and experienced both solitude and socializing. I can't complain.