Cabrillo's Inner Beach is located inside the breakwater and at the doorstep of the Cabrillo Aquarium. The breakwater prevents most waves and longshore transport from entering the harbor. The waves along this beach are very small and of extremely low energy. Thus, the sediment found on the Inner Beach is a very fine sand and the beach face is very flat. The sand is composed of mineral fragments (quartz, potassium feldspar, plagioclase feldspar, biotite and occasionally hornblende) derived from the mechanical weathering of rocks, most likely from the San Gabriel Mountains. Like the Outer Beach, this beach sand must be replenished every seven years or so.
Additionally, the breakwater prevents longshore transport from occurring along the coast behind it and restricts water circulation within the harbor. This can lead to a build-up of sand in undesirable areas, and unhealthy water conditions in others.
Photo looking southeast.