Mostly fire roads, but there are cow paths that go down to the beach, Vandenberg Air Force Base owns some of the land out there, but there is also a state park out there as well.
Head on Betteravia west from 101 about 10 miles. Betteravia will split just outside of town. Left is Mahony Road and Betteravia continues right, so right, another couple of miles. You will pass Black Rd. and Roy Rd. Eventually you will get to Brown Rd. take a left on Brown Rd. to head West. Take Brown all the way to the end and park in front of the small concrete barrier. Off to the right will be a gate with a short paved road. Lift your bike over the fence ( it is closed to autos due to wash outs) and start climbing the hills, there are several single track trails that will lead you to the beach. There are great views.
http://www.singletracks.com/item.php?c=1&i=1896