This is a good trail run as long as you don't mind the elevation gain.
This trail starts at Eldorado Canyon State Park. Drive to the visitor's center and run north from there.
The trail climbs steadily through several switchbacks. After an hour or so it will flatten out and then descend to South Boulder Creek. From there, you can join the Walker Ranch
trail. Watch out for bikes at the trail junction.
Eldorado Canyon is very popular with hikers and rock climbers. It will be crowded on weekends. Get there early to avoid the crowds.