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This 1994 article appeared in a publication produced by the United States National Parks Service.
Illustrations and content were provided by the City of Los Angeles Stormwater Program.

Illustrations by: Oscar Amaro Written by: Chuck Ellis, Angela Franklin


Approximately ten million years ago the area that is now Los Angeles was completely under water. Over time mountain ranges were uplifted and then gradually eroded to form the floors of the San Fernando and San Gabriel valleys.

As far back as 50,000 years ago, small groups of people inhabited the Pacific coastal plain. It is estimated that the ancestors of the most recent American Indian inhabitants, part of the Shoshonean language group, migrated to the area about 1,500 years ago. The name the tribe used for themselves is not recorded, but today their descendants go by the name Tongva.

These people thrived in the mild climate with rich natural resources, and by the 1770’s when European explorers first arrived in California; they had established over 40 villages throughout the area from Topanga Canyon to Laguna Niguel. Their way of life was interrupted by the arrival of the explorers. With the founding of the San Gabriel Mission in 1771, the native residents of this area were identified as the Gabrielino, because of their association with the mission.

A Pueblo is Founded and Flourishes

In 1769 the expedition of Don Gaspar de Portola brought the first European explorers to Southern California. Traveling with this group was a Spanish priest, Father Juan Crespi, who recorded the first written description of the river: "…through a pass between low hills, we entered a very spacious valley, well grown with cottonwoods and alders, among which ran a beautiful river from the north-northwest." De Portola’s party camped along the river near Elysian Park. Having arrived on the jubilee celebration of our Lady of Los Angeles de Porciuncula, they named the river Rio de Porciuncula.

Twenty-one years later, on September 4, 1781, settlers commissioned by the governor of Mexico came to this location to found El Pueblo de Nuestra Senora la Reina de Los Angeles. Unlike what may be expected, historians tell us that these first settlers were not all Mexican or Spanish; they included people of American Indian and African heritage as well as 24 children, foretelling the diversity that uniquely defines Los Angeles today.

  Like many other great cities built along major waterways, Los Angeles prospered, and from its infancy was considered prime real estate for settlers looking for opportunity. The river became a center for growth as more and more people depended on it for fresh drinking water and crop irrigation. Along with the people, many other forms of life flourished in the river and on its banks. Sycamore, alder and cottonwood trees formed a cool and green canopy over the river, and oaks dotted the upland terraces. Hundreds of species of birds thrived in the river habitat, including the now rare yellow-billed cuckoo, and several kinds of heron. Migratory ducks and shore birds welcomed a resting spot on the riverbanks during their yearly migrations, and steelhead trout swam upstream from the Pacific Ocean to spawn.

In an effort to further promote growth in the pueblo, Spanish and later Mexican law required that water supplies be established and maintained. Community-owned irrigation networks, called zanjas, were built to supply residents with water from the Los Angeles River. However, by 1900 the pueblo had become a city of over 100,000 people and water supply became a critical concern. The zanjas could no longer supply the quantity of water needed by the growing population, so by the early 1900s an aqueduct was constructed to bring water from the Owens Valley – some 250 miles north.



Flooding is a natural occurrence with all rivers and the area covered by these flows is known as the floodplain. Until this century, the Los Angeles River flowed freely within its natural banks. Periodically, heavy rains would cause its waters to overflow the banks and spread for miles across the coastal plain until they eventually reached the ocean or drained into the ground to replenish the groundwater, or aquifers.

Until 1825, the river’s course flowed east from the Sepulveda Basin, southeast through Glendale narrows, south through the Pueblo (Downtown), then west along what is now Washington Boulevard and into Santa Monica Bay. But that year, excess in sediments deposited during a huge storm caused the river to dramatically change its course; instead of traveling west from Downtown, it flowed south towards San Pedro Bay.