Geologic map shows successively younger strata towards the coast. The Oakville and Fleming units (blue) are of Miocene Age (5.3 to 23 million years old). The Goliad is Pliocene (3 to 5.3 million years old), the Willis is Late Pliocene to Early Pleistocene (800,00 to 3 million years old), The Lissie and overlying units are Middle Pleistocene to Holocene (less than 800,000 years old).