The Cabo Rojo beach-ridge plain was formed in a low-energy shadow behind the Blanquilla-Lobos coral-reef tract. The source of the sand comprising Cabo Rojo was offshore material of Wisconsin (?) age, most probably deposited by the Rio Panuco during a lower sea-level stand. Islands within the Laguna de Tamiahua define a sandstone body similar in shape and orientation to that of Cabo Rojo, strongly suggesting either a 2-stage Holocene constructional history, or the remains of a pre-Wisconsin barrier.

The beach-ridge plain consists of low, hummocky ridges (relief less than 1 m, spacing of 100 m) oriented parallel with the present coast. This coast is undergoing erosion, and beach ridges are not forming. Cliffed, back-beach dune ridges are found on the northern and

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southern parts of Cabo Rojo, the northern ridges being best developed. Longshore drift compartmentalization has been effected along this coast by the Blanquilla-Lobos offshore reef tract.

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