They form the craggy outcrops. These blocks sit in soft matrix of sheared shale and serpentine which is easily eroded into grassy slopes. This creates a topography that looks like slightly melted ice cream. Each of the hard blocks is a very different rock type born on the ocean floor many miles from here. The spreading ocean floor carried them to the continent where subduction faulted , deformed, and mixed them up.
Most geologists agree that it forms when one plate slides underneath another in a subduction zone.
Melange may also form along great fracture zones in ocean crust, where movement is dominantly horizontal. Soft-sediment landslides on the ocean floor can also mix rocks but they usually consist of rocks of the same type. At Shell Beach we see fragments of originally continuous sedimentary layers, metamorphic rocks, volcanic and plutonic igneous rocks. Original rocks range in age from 150-100 million years. The subduction and mixing occurred between 100 and 10 million years ago.