The non native settlement of the site began in 1850 as a camp with a one-room sod warehouse as the U.S. Army Depot Vallecito for the supply of Fort Yuma.

After crossing the desert from Hawi, the trail ran up Oriflamme Canyon to Cañada Verde, (or Green Valley as it came to be called by later American settlers) in the Cuyamaca Mountains.

As many as twenty springs are concentrated near the camping ground; these ooze out gently, flow down a few yards as a small stream, and then sink into the soil.

In 1846, Colonel Stephen Watts Kearny and his dragoons with their scout Kit Carson passed through Vallecito on their route from New Mexico to California.

The Southern Immigrant Trail became the highway for the Forty-Niners to California; it was also a major route for herds of cattle and sheep from Texas and New Mexico on their way to the goldfields.

[6] The sod building of Depot Vallecito was subsequently taken over in 1854 and expanded by a settler named James Ruler Lassator (also spelled Lassiter and Lassitor in various public records and secondary sources) and lived there with his wife Sarah and his stepsons, Andrew and John Mulkins.

The Lassators raised their children there, operated a store, and provided a campground for travelers coming across the Colorado Desert in the Southern Immigrant Trail.

[5]: 79–95 Between 1854 and 1857, military couriers taking mail between San Diego and Fort Yuma used the old native route through Vallecito and Green Valley.

In 1857, Lassator and his stepson John Mulkins also began a 160-acre ranch in Green Valley in the Cuyamaca Mountains to the west of Vallecito.

Lassator's Green Valley ranch became his home and the site for annual rodeos after he was appointed Judge of the Plains for Agua Caliente Township.

Travelers willing to take mules could descend or ascend Oriflamme Canyon between Lassitor's Green Valley ranch and Carrizo Creek Station.

Vallecito was an exception; pasturing livestock for other desert changing stations, it had two hostlers providing meals, a cook, and a merchant residing at the store there.

Several short-lived stage lines that ran from Los Angeles and San Bernardino to Arizona used Vallecito, as well as most of the other old overland mail stations.

[5]: 79–95 Charles Ayres, a former postmaster at Warner's Ranch from 1870 to 1875, and his family settled at the abandoned station of Vallecito where he raised cattle and mules.

James E. Mason visited the area on a prospecting trip in 1878 and settled at Vallecito, keeping cattle with Ayers' livestock.

With funds from the county and State Emergency Relief Agency, a nearby rancher Everett Campbell supervised the reconstruction of the old stage station.