East of Santa Barbara, the Tunnel Trail is a popular ride. It is an out-and-back ascent up about 2,500 feet of vertical. It is a really downhillers route that is rocky and loose.
To reach the Tunnel Trail trailhead from US101, use the Mission Street exit. Head northeast and turn right on Foothill Road. Then turn left on Tunnel Road. Continue on Tunnel Road to the trailhead gate.
Note: this is mountain lion country, so keep your eyes open. Also, while this route is dominated by mountain bikers, watch out for the occasional hiker. The route can be very buggy and humid in June and July.
Overall, Tunnel Trail is the 128th most popular mountain bike trail of all 132 mountain biking rides in California.