Half Moon Bay is a 6.5 mile shoreline between the rocky headlands of Pillar Point and Miramontes point. The broad beaches are composed of loose sand and gravel and are backed by a narrow coastal terrace. Prior to 1959, seacliff retreat was low because sand that periodically eroded from the cliffs would accumulate on the broad beaches. As a result, the cliffs became protected from further erosion.

In 1959, a riprap breakwater was constructed at the north end of Half Moon Bay near Pillar Point. A breakwater is usually constructed to protect a harbor from wave action. However, cliff erosion and property damage inside the harbor were not eliminated. Instead, the breakwater disrupted wave patterns and caused accelerated cliff erosion. The new wave patterns did not allow the sand to accumulate on the beaches. Roads, utilities and private property are now threatened by seacliff retreat of nearly 3 feet per year in some places.

In the pictures below, the once broad beaches are now very narrow. The rocky cliffs are minimally buffered by the sand.

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