A better access point than trying to enter via the Highway 68 overpass. Plenty of parking, and access via public land.
Park at the overflow parking for the Creekside Terrace entrance of the Fort Ord National Monument. Follow a use trail down to Toro Creek, which is almost always dry. There is some Poison Oak. Once in Toro Creek, turn left (north) towards the Salinas River 1/4 a mile. This entrance is on BLM land.