The Los Angeles River begins at the confluence of Bell Creek and Arroyo Calabasas, which drain from the Simi Hills and Santa Monica Mountains respectively, and flows southeast for 30 miles (48 km) through the San Fernando Valley and downtown Los Angeles, then south for another 20 miles (32 km) to San Pedro Bay at Long Beach, California. Once free-flowing across a broad alluvial fan, the river now runs in a concrete channel—built after devastating early 20th-century floods. Development in Long Beach has so altered the original coastal landscape that little remains natural. Its main physiographic features are now low hills and mesas shaped by the Newport-Inglewood structural zone. Identified as a groundwater barrier since 1905 and an oil trap since 1921, this zone lies within the Los Angeles sedimentary basin. Beneath Long Beach are about 14,000 feet (4,267 m) of Miocene and Pliocene sediments, underlain by unknown depths of pre-Miocene rock. Overlying units include the San Pedro Formation, terrace deposits, Palos Verdes sand, and coastal alluvium. Oil revenues once helped modernise Long Beach’s port and economy, though drilling caused 29 feet (8.8 m) of subsidence. A magnitude 6.3 earthquake struck offshore along the Newport–Inglewood zone in 1933—the city’s largest recorded seismic event. Long Beach’s early water supply came from artesian wells and springs. As groundwater declined, pumping was needed, and supplies were drawn from sources up to 400 miles (640 km) away. Over-pumping from four aquifers allowed saltwater intrusion from the Pacific. Since 1970, injection programs have created a freshwater barrier to halt chloride advance. The city’s southwestern shoreline hosts the Port of Long Beach, built largely from dredge-fill and armour rock, and protected by an 8.2-mile (13.1 km) breakwater.

The archaeological record suggests that this coast has been inhabited for over 10,000 years, with several successive cultures settling 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. The river provided them with water and food. The Tongva were hunters and gatherers who lived primarily on fish, small mammals, and acorns from the abundant oak trees along the river. At least 45 Tongva villages were located near the Los Angeles River. After Spanish colonists arrived and established Mission San Gabriel in 1771, they referred to the Tongva in the area as Gabrieliño. Most were relocated to missions by the mid-19th century, and their population declined drastically due to exposure to European diseases. In 1784, King Carlos III of Spain granted Rancho Los Nietos to Spanish soldier Manuel Nieto. 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 ordered its division into six smaller ranchos, including Rancho Los Cerritos—meaning ‘little hills’—whose lands encompassed present-day Cerritos and Long Beach. In 1843, Jonathan Temple purchased Rancho Los Cerritos and built what is now the Los Cerritos Ranch House, a still-standing adobe structure. He sold the property in 1866 to a sheep-raising company. The land later passed to the Bixby Land Company, then to a Los Angeles syndicate known as the Long Beach Land and Water Company. The name of the community was changed to Long Beach, and the city was officially incorporated in 1897.

Long Beach developed as a seaside resort with some light agriculture. Signal Hill, the area’s most prominent topographic feature at 365 feet (111 m), offers views of the Los Angeles harbor and was initially considered for upscale residential development. In 1916, Union Oil Company of California drilled the first exploratory well, Bixby I, to a depth of 3,449 feet (1,051 m). In 1921, Shell Oil Company struck oil with the Alamitos I well on the southeast flank of Signal Hill at 3,114 feet (949 m), producing 483 barrels per day. Soon, the 1,400 acres (567 ha) of Signal Hill were covered in oil derricks. The site became the richest oil field in US history, and Los Angeles County emerged as the world’s fifth-largest oil producer. Later in 1921, Shell discovered the Wilbur I zone—above the interval reached by Alamitos I—which initially produced 36 barrels of oil and 7 billion cubic feet of gas per day. In 1922, the deeper Brown zone was found below Alamitos I. The field eventually extended about 3 miles (4.8 km) long and 1 mile (1.6 km) wide. That year, the Petroleum Midway Company’s Ryder I well yielded 3,650 barrels per day. Combined production from the Alamitos, Wilbur, and Brown zones peaked at 259,000 barrels per day in 1923. By 1957, the California Division of Highways began acquiring and abandoning wells along the planned route of the San Diego Freeway. As of 2000, the Long Beach oil field had produced nearly 1 billion barrels of oil from 1,725 acres (698 ha)—over 500,000 barrels per acre—with more than 14 million barrels estimated to be recoverable. Read more here and here. Explore more of Los Angeles River and Long Beach here: