"Gravel ginding" is becoming an increasingly popular for of cycling recreation. It's not rocky singletrack MTB riding. It's gravel roads, rails to trails, etc riding and is done solo, organized rides and races. In Phoenix, we have an extensive canal trail system.
Here are a couple of quick cell phone shots of one of mine -- one of my 1989 Trek 660's converted over the weekend to single speed with 30mm cyclocross tires. It's first ride -- 30 miles of canal paths -- was a success. A very lively ride.