The South Gabriel Post Office opened in Postmaster Thomas Lewiston's mercantile store on Sept. 29, 1871. The village, named for the South San Gabriel River, was also called Lewiston.
Located on the Austin-Burnet Road, the hamlet soon had two stores, a hotel, saloon, cotton gin, school, church, and wagon, saddle, blacksmith, and carpentry shops. The population in 1880 was 39.
The Austin and Northwestern Railroad passed to the north of the settlement in 1882, and on Dec. 8, 1882, the post office moved to the new town of Bertram (2 miles N) and South Gabriel disappeared.