Los Angeles River starts at the confluence of Bell Creek and Arroyo Calabasas that drain from the Simi Hills and Santa Monica Mountains respectively, and flows generally southeast for 30 miles (48 km) through the San Fernando Valley and downtown Los Angeles and then south for 20 miles (32 km) to San Pedro Bay at Long Beach, California. While the river was once free-flowing across the broad alluvial fan that is now the City of Los Angeles, it is currently notable for flowing through a concrete channel on a fixed course, which was built after a series of devastating floods in the early 20th century. The development of the City of Long Beach has altered the original coastal landscape to such a degree that little remains in its natural state. Dominant physiographic features within the city are now only present in the form of small hills and mesas associated with the faults and folds of the Newport-Inglewood structural zone. This zone has been recognized as a ground-water barrier since 1905, and as a structural crude oil trap since 1921. The city lies within the Los Angeles sedimentary basin and rests on top of about 14,000 feet (4,267 m) of Miocene and Pliocene sediments and an undetermined thickness of pre-Miocene basement rocks. Pleistocene to Holocene surficial geologic units overlie these oil-producing zones. These rock units include the San Pedro Formation, terrace deposits, the Palos Verdes sand, and alluvial and coastal deposits. Oil revenues enabled Long Beach to modernize its port and coastal commercial enterprises; however, oil extraction has caused approximately 29 feet (8.8 m) of ground subsidence. In 1933, a magnitude 6.3 earthquake occurred offshore along the Newport-Inglewood structural zone and remains the largest seismic event recorded in the city. Artesian wells and springs first supplied all of the city’s water requirements, but with time, groundwater levels were drawn down such that pumping was required. At the present time, additional water supplies come from as far away as 400 miles (640 km). Excessive pumping of groundwater from four major aquifers has caused salt-water intrusion from the Pacific Ocean. Water injection programs, in force since 1970, have created a fresh-water barrier halting further chloride advance. The southwestern shoreline of the city consists of the Port of Long Beach, constructed almost entirely of dredge-fill and armor rock. The entire shoreline is protected by a breakwater 8.2 miles (13.1 km) long.

The archaeological record suggests that this coast has been inhabited for over 10,000 years, and several successive cultures have settled in the area of present-day Long Beach. By the 16th century when Spanish explorer Juan Rodriguez Cabrillo arrived, the dominant group was the Tongva people and the river provided a source of water and food. The Tongva were hunters and gatherers who lived primarily off fish, small mammals, and the acorns from the abundant oak trees along the river’s course. There were at least 45 Tongva villages located near the Los Angeles River. After the arrival of Spanish colonists and the establishment of Mission San Gabriel in 1771, the Spanish referred to all of the Tongva living in that mission’s vicinity as Gabrieliño. Most of the Gabrieliño relocated to Spanish missions in the mid-19th century resulting in a drastic drop in population from exposure to European diseases. In 1784, the Spanish King Carlos III granted Rancho Los Nietos to Spanish soldier Manuel Nieto and it was one of the first, and the largest, Spanish land concessions in Alta California. The rancho remained intact until 1834 when Mexican Governor Jose Figueroa officially ordered its partition into six smaller ranchos including Rancho Los Cerritos, where ‘Cerritos’ means ‘little hills’ and the rancho lands included the present-day cities of Cerritos and Long Beach. In 1843, Jonathan Temple bought Rancho Los Cerritos and built what is now known as the Los Cerritos Ranch House, a still-standing adobe building. In 1866, Temple sold Rancho Los Cerritos to a sheep-raising company, and eventually, the land was passed on to the Bixby Land Company and then to a Los Angeles syndicate that called itself the Long Beach Land and Water Company. They changed the name of the community to Long Beach and the city was officially incorporated in 1897.

The town of Long Beach grew as a seaside resort with light agricultural uses. Signal Hill is the most prominent topographic feature in the area with an elevation of 365 feet (111 m) which allows a view of the Los Angeles harbor and was originally considered for development into expensive residential lots. In 1916, the first exploratory well was drilled by Union Oil Company of California and called Bixby I that extended to a depth of 3,449 feet (1,051 m). In 1921, Shell Oil Company drilled a discovery well called Alamitos I on the southeast flank of Signal Hill to a depth of 3,114 feet (949 m) that produced 483 barrels of oil per day. The 1,400 acres (567 ha) of Signal Hill were soon covered by oil derricks and this became the richest oil field in U.S. history and Los Angeles County became the world’s fifth-largest oil producer. Later in 1921, Shell Oil Company discovered a productive zone called Wilbur I above that was encountered by Alamitos I that would initially produce 36 barrels per day and 7,000 million cubic feet of gas. In 1922, the Brown zone situated below Alamitos I was discovered, and the field would be extended to about 3 miles (4.8 km) long and 1 mile (1.6 km) wide. The Petroleum Midway Company drilled a well called Ryder I that produced at a daily rate of 3,650 barrels. The Alamitos, Wilbur, and Brown zones would reach a peak of 259,000 barrels of oil per day in 1923. By 1957, the California Division of Highways began acquiring and abandoning wells along the proposed route of the San Diego Freeway. As of 2000, the Long Beach oil field has produced nearly one billion barrels of oil from 1,725 acres (698 ha), or over 500,000 barrels of oil per acre, with over 14,000,000 barrels of oil estimated to still be recoverable. Read more here and here. Explore more of Long Beach and the Los Angeles River here: