From the USDA Forest Service Site:

The Cleveland National Forest is the southern-most National Forest in California. Consisting of 460,000 acres, the forest offers a wide variety of terrains and recreational opportunities.

Until the arrival in San Diego of Juan Rodriguez Cabrillo, the lands now within the Cleveland National Forest were known only to the desert and coastal Indian tribes who used them. The Kumeyaay, Luiseños, Cahuilla and Cupeño found a good living on the abundant acorns and game. Many of our trails today follow those routes first used by these early dwellers.

Cabrillo's arrival in 1542 had little affect on the area. It wasn't until 1769 that the Peninsular Range and its coastal plain attracted much interest. Fearing possible interference by England and possibly Russia, Spain encouraged Junípero Serra to establish his first of 21 California Missions.

The original site of the first mission was located near the present Old Town in San Diego. It was constructed in part by timbers hauled in from what is now Rancho Corte Madera (wood yard), on the Descanso Ranger District. Further north, timbers from Los Piños Potrero (on the Trabuco Ranger District) were hauled down toward the coast to build Mission San Juan Capistrano.

Also in that year, the Portolá expedition, led by Gaspar de Portolá and joined by Juan Crespí, Francisco Gómez, and Pedro Fages, left San Diego traveling to Monterey. They named many of the places along the way and those names remain with us today.

Prior to the establishment of the missions, human impact on the land was relatively insignificant. The explorers Vizcaíno and Cabrillo reported that the native Indians did considerable burning of the brushlands along the coast and in the mountains, but the overall impact was probably not very great. However, with the arrival of a ranching culture, the landscape underwent more dramatic changes; subtle at first, as the native grasslands were slowly replaced by European and Asian weeds and other introduced plants. Some botanists argue that this invasion of exotic plants had more affect on the area than any other single factor.

During the 1700's the land had been parceled out in large land grants. One of these, the Rancho San José del Valle grant, was given in 1844 to one of the earliest settlers, a fur trader named J. T. Warner. About the same time, Juan Forster received the land grants of Los Piños Potrero, El Cariso Potrero, and Potrero de la Cienega.

Widespread overgrazing throughout the area, brush and trees cut for fence posts, and fires set to produce forage expanded the impact well beyond that of the Indians in the previous centuries.

In 1869, gold was discovered near Julian attracting hordes of miners from the Mother Lode and swelling the town to a population greater than that of San Diego. Also, during this period, zinc, lead, and silver mines were booming in the western canyons of the Santa Anas (hence, Silverado Canyon). Nearby, in Trabuco Canyon, stands the remains of the large (and unproductive) tin mine, once owned (about 1900) by Gail Borden of the Eagle Milk Co. He had hoped to use its yield to produce cans for his milk.

The influx of miners left its mark on the land. Trees were cut for mine timbers, heat and cooking fuel. Great expanses of brush were burned so miners could penetrate new areas to search for minerals.

As the mines petered out, so did many of the early ranches which had been overgrazed and had lost their chief labor force as the Indian population died off due to hardship and disease.

The principal end results was steadily growing threats to the watersheds, which by now were of critical importance to southern California communities.