In 1961, 1962, and 1963, surveys of part of the "black sand" beach at Malaga Cove, California, included profiles for measuring seasonal variations in beach erosion and accretion, and sampling for grain-size, mineral composition, and magnetite percentage.

Profiles show maximum beach erosion during August and maximum accretion during January, contrary to the cycle of summer accretion and winter erosion for most beaches.

Mean grain-sizes, determined from analyses of samples extracted on October 19, 1963, are largest for all depth intervals within a narrow strip midway between the cliff and the swash. Particle size gradually decreases both oceanward and shoreward and increases northward. The average percentage of magnetite decreases with an increase in grain-size.

Magnetite, ilmenite, epidote, zircon, and quartz are the most abundant of 27 minerals identified petrographically in the very fine size.

For all samplings, the magnetite content in the beach sand increases with depth and shoreward; maximum concentrations are at the "slope break" near the cliff. During beach buildup, high-energy waves temporarily erode the foreshore, carry the lighter, fine materials offshore, and concentrate the magnetite and other heavy minerals as laminations and layers at depth in the beach. The magnetite concentration high on the beach reflects the superiority of onshore wave energy over other types of wave energy.

The magnetite and ilmenite in the sand at Malaga Cove are believed to have been transported from the western San Gabriel Mountains to Santa Monica Bay when the Los Angeles River channel followed the present course of Ballona Creek. The minerals were carried southward along the coast by predominant littoral movement in this direction and concentrated by wave action on the beach at Malaga Cove.

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