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San Joaquin River

geography Maturity 7-9 Next article →

The San Joaquin River is the longest river in Central California.

San Joaquin River headwaters 2
San Joaquin River headwaters 2

It serves as a vital lifeline for the region's agriculture and wildlife. The river provides essential irrigation water for crops in the San Joaquin Valley. It also acts as a critical wildlife corridor for many species. However, the river is also one of the most heavily dammed and diverted rivers in California. This means human engineering has significantly changed how the water flows through the landscape.

The river's journey begins in the high Sierra Nevada mountains.

San Joaquin River headwaters 3
San Joaquin River headwaters 3

Its source is located within the Ansel Adams Wilderness. The river forms at the confluence, or meeting point, of three major branches called forks. These are the Middle Fork, the North Fork, and the South Fork. The Middle Fork is the largest of these three branches.

San Joaquin River headwaters 2
San Joaquin River headwaters 2

From these alpine headwaters, the water flows south through the mountain foothills. It passes through four hydroelectric dams, which are used to generate electricity from moving water.

After leaving the mountains, the river enters the San Joaquin Valley. It emerges from the foothills near the site of the former town of Millerton. Since 1942, the Friant Dam has been located here, creating Millerton Lake.

Millerton Lake 1
Millerton Lake 1

As the river flows west-southwest, it passes north of the city of Fresno. Much of the water is diverted into aqueducts, which are man-made channels used to move water. Because of these diversions, a 150-mile section of the river frequently runs dry. This dry stretch exists between Friant Dam and Mendota.

The geology of the river changes as it moves downstream. The upper segment is a steep, rocky mountain stream. It flows over granitic igneous and metamorphic rock from the Mesozoic Era.

San Joaquin River headwaters 2
San Joaquin River headwaters 2

In contrast, the lower segment is a meandering stream. It flows over alluvial deposits, which are layers of sediment left by water. These deposits make up the flat floor of the Central Valley. Millions of years ago, this valley was actually an inland sea. The movement of the North American and Pacific Plates created the basin we see today.

Human history in this valley stretches back thousands of years. Archaeological evidence suggests people arrived in the region between 12,000 and 5,000 years ago. The southern Yokuts people called the river Tihshachu, meaning "salmon-spearing place."

Bierstadt Albert Mariposa Indian Encampment Yosemite Valley California
Bierstadt Albert Mariposa Indian Encampment Yosemite Valley California

In the early 1800s, Spanish explorer Gabriel Moraga surveyed the area. He named a tributary after Saint Joachim. By 1810, the name "San Joaquin" was in common use for the entire river. Later, settlers from Spain and America arrived in the basin.

The river's flow has changed drastically due to 20th-century engineering. Many dams and levees were built on the river and its tributaries. These structures changed the river's natural fluctuations. They also cut off the Tulare Basin from the San Joaquin watershed. Historically, the river supported millions of migratory birds and hundreds of thousands of spawning salmon. Today, federal agencies regulate the water for navigation and supply. This regulation has dramatically reduced the amount of water flowing through the river.

As the river nears the ocean, it meets several large tributaries. These include the Tuolumne, the Stanislaus, the Calaveras, and the Mokelumne rivers. Near the city of Stockton, the river is part of a navigation project.

StocktonDeepwaterShippingChannel
StocktonDeepwaterShippingChannel

This project created the Stockton Deep Water Ship Channel to allow ships to pass. The river eventually joins the Sacramento River at Antioch. This meeting forms the head of Suisun Bay. From there, the water flows through San Francisco Bay and into the Pacific Ocean.

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🖼️ Images & Media (15)
File:San Joaquin River Viaduct aerial 2016.jpg
San Joaquin River Viaduct aerial 2016.jpg
File:SanJoaquinMendotaPool.jpg
SanJoaquinMendotaPool.jpg
File:San Joaquin River headwaters 2.jpg
San Joaquin River headwaters 2.jpg
File:Bierstadt Albert Mariposa Indian Encampment Yosemite Valley California.jpg
Bierstadt Albert Mariposa Indian...
File:Mount Diablo California from Concord.jpg
Mount Diablo California from Concord.jpg
File:Stockton California circa 1860.jpg
Stockton California circa 1860.jpg
File:Californiacentralvalley.jpg
Californiacentralvalley.jpg
File:Mammoth-Pool.jpg
Mammoth-Pool.jpg
File:StocktonDeepwaterShippingChannel.jpg
StocktonDeepwaterShippingChannel.jpg
File:CVPSouthernCanalsUSBR.jpg
CVPSouthernCanalsUSBR.jpg
File:Millerton Lake 1.jpg
Millerton Lake 1.jpg
File:San Luis National Wildlife Refuge.JPG
San Luis National Wildlife Refuge.JPG

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