Vernalis is an unincorporated community in San Joaquin County, California, United States. Vernalis is located on California State Route 33 10.5 miles southeast of Tracy. Vernalis has a post office with ZIP code 95385. The first post office in the area opened under the name of San Joaquin in 1851; that post office closed in 1852, reopened in 1874, and was moved 3 miles southwest in 1888, after which its name was changed to Vernalis.