Civilians established a small farming settlement called Calabasas, in the area nearby the protection of the Presidio.

Following the Gadsden Purchase, the United States Army stationed Major Enoch Steen and four companies of the 1st U.S. Dragoons, now the 1st U. S. Cavalry, at old Camp Calabasas on November 27, 1856.

During the American Civil War, Calabasas was briefly occupied by the Confederates in March 1862 before the arrival of the California Column in April.

The Regulars abandoned Fort Mason due to persistent malaria in the fall of 1866 and established Camp Cameron.

[1] All these posts were located south of the confluence of Potrero Creek and the Santa Cruz River.