On the west side of the Point Loma peninsula are west facing sandstone cliffs from which Sunset Cliffs got its name. The cliffs are sheer and are undergoing constant erosion caused by wave action. Geologically these cliffs are known as the Point Loma Formation. It extends into the ocean to form a sea bed. They contain fossils, including dinosaur fossils, from the late cretaceous period, about 75 million years ago. The formation represents one of the few sites of dinosaur fossils in the state of California. The Point Loma Formation also contains concretions. On top of this is another late cretaceous deposit called the Cabrillo formation.
Above the cliff tops, the upland portion of the park is fairly flat with an elevation of about 400 feet. This area consists of a much younger sandstone and conglomerate deposits from the Pleistocene era, 1 million years or less in age. These flat-lying beds lie directly on top of the gently dipping Point Loma and Cabrillo formations. The gap in the sedimentary record, called an angular unconformity, represents about 70 million years of non-deposition and/or erosion.