Located about 15 minutes West of Discovery Bay off of Marsh Creek Road. Round Valley Regional Preserve is a small trail system with about 6 miles of trails (for a 12 mile out and back). If you are looking for a longer ride there are connectors to the Los Vaqueros trails and to the Morgan Territory Regional Preserve. If you decide to venture into Los Vaqueros there is a trail use fee. Althought the trails in Round Valley aren't very exciting there are lots of hills to get a workout on and they also link up to miles of trails in other systems (clear over to Mt Diablo) so you can really get a good workout in.
All of the rides in this area are pretty similar, essentially bulldozed fireroads over rolling hills. You can go quite fast on the fireroads but other than loose steep hills don't expect to challenge your riding skills. There is also very little tree coverage so it is very hot in the summertime. I like Round Valley a little better than Los Vaqueros because there are more trees and the surroundings are a little nicer. There is also some cool old farm equipment near the halfway point of the trail. I spotted a coyote at while riding here.
From Discovery Bay head West on Hiway 4 to Marsh Creek road. Turn Left on Marsh Creek and look for a trailhead on your left (about 2-4 miles). Maps are available at the trail head as are several restrooms. Lots of horseback riders frequent these trails but there is plenty of room to share.
Ok, here he is, not a great shot but what the hell. The coyote is just to the left of the tree almost dead center of the shot.