Park at 15th Ave and Wedemeyer St at the Presidio Landmark and take the Lobos Creek Valley Trail down to the beach. You can walk on the beach almost all the way to the north end, but the last exit is the 'Sand Ladder' a few hundred yards before that.

The trail leads you back to Washington Blvd in the Presidio. Make a right on Battery Caulfield Rd to get back to the parking location.