Boca de Santo Tomás is at La Bocana, where the Santo Tomás valley reaches the coast south of Ensenada. There is a right-hand point, rocky beach peaks and a river mouth, and the headland and kelp can keep it cleaner than the open coast when the wind picks up. It is a camping trip more than a day trip.
Follow the signs for La Bocana and Punta China off Highway 1 south of Ensenada. The dirt road is rough, so a high-clearance vehicle is recommended. Stock up on food and water in Ensenada.