Fresnosaurus is an extinct genus of plesiosaur from the Late Cretaceous (Maastrichtian stage) of what is now California.

The type species is Fresnosaurus drescheri, first described by Welles in 1943.

[1] The generic name Fresnosaurus honors Fresno County, while the specific name honors Arthur Drescher.

[2][1] Fresnosaurus was probably at least 9 meters (30 feet) in length.

Like all elasmosaurid plesiosaurs, it probably ate small bony fish, belemnites, and ammonites.