Overlooked by the expedition of Juan Bautista de Anza, the largest natural lake in Southern California was first seen by the Spanish Franciscan padre Juan Santiago, exploring eastward from the Mission San Juan Capistrano in 1797. In 1810, the water level of the "Laguna Grande" was first described by a traveler as being little more than a swamp about a mile long. Later in the early 19th century, the lake grew larger, providing a spot to camp and water their animals for Mexican rancheros, American trappers, the expedition of John C. Frémont, and the immigrants during the California Gold Rush as they traveled along the southern shore of the lake on what later became the Southern Emigrant Trail and the route of the Butterfield Overland Mail.