The middle half of California is dominated by the towering Sierra Nevada ranges to the east and the Coast Ranges to the west. In the center is the aptly named Central Valley. This valley is known for its agricultural productivity and horticulture. It provides around half or more of the vegetables, nuts, and fruit grown in the United States.

But this fertile valley has an interesting geologic history of its own - one that was shaped by the mountains around it. It was once a large inland sea that was home to prehistoric animals that have long since vanished. The large prehistoric sea of North America was the massive Western Interior Seaway that once flooded the Great Plains and was full of rich marine life.

UPDATE: 2023/02/04 15:50 EST BY AARON SPRAY

The Ancient Sea In The Central Valley Was Not The Only Prehistoric American Body Of Water

The Central Valley, as an ancient inland sea, is not unique in North America. There were other ancient seas and ancient lakes. This article was expanded with more of the prehistoric lakes and bodies of water - some of which were as recent as human times in North America. Visitors can see the marks of these bodies of water if they know what to look for.

The Central Valley: Size, Formation, And Prehistoric Sea

The Central Valley is around 40 to 60 miles wide and stretches for around 450 miles, and covers around 18,000 sq miles. It occupies around 11% of the area of California and includes the state capital of Sacramento. Other cities include Redding, Chico, Stockton, Modesto, Merced, Fresno, Visalia, and Bakersfield.

  • Width: 40 to 60 Miles
  • Length: 450 Miles
  • Size: 18,000 sq miles

The flatness of the valley is a stark contrast with the rugged hills and gentle mountains that surround it. It has been enclosed by the uplift of the Coast Ranges, and over the millennia, the valley filled with sediments flowing down into it and has filled it in overtime. It was these sediments that caused it to become so flat.

  • Sediments: Have Filled The Central Valley Sea In Over Millions Of Years
  • Flatness: Because of The Sediments That Have Washed Into It

The sediments are now thousands of meters deep and began during the Cretaceous period around 80 million years ago. It had been filled in by enough sediment to become mostly dry land by around 1.5 million years ago. It is believed that the Great Valley Sea continued for long in the San Joaquin Valley than the Sacramento Valley.

  • Vanished: The Last Of The Central Valley Disappeared around 1.5 Million Years Ago

In the past, it is thought that the Central Valley was an inland sea. In fact, because the Central Valley is so low-lying, before California's flood control and aqueduct system was built, annual snowmelt turned much of the valley into something of an inland sea.

Related: 10 Restaurants You Must Visit In California (& Their Most Popular Dish)

The Central Valley's Walrus

Today all the walrus species only live in the Arctic regions far to the north. They can be found in the Canadian high arctic, Greenland, Siberia, and Alaska. But the Central Valley once had its own species of Walrus, win it was an inland sea.

  • Pliopedia pacific: The Species Of Walrus Discovered In the Central Valley
  • Lived: Late Miocene
  • Discovered: In 1909

The species of walrus ground in what is now the Central Valley is called Pliopedia pacific. It is believed to have lived in the late Miocene and was first known from a holotype specimen (USNM 13627) that was collected in 1909 by Robert Anderson.

Fossils of these Californian walruses were found in the Paso Robles Formation of San Luis Obispo County in the valley. The Paso Robles Formation is known for preserving many fossils that date back as long ago as 23 million years ago.

Related: Bucket List Destinations For Families Traveling Through California

Visiting The Central Valley

Today there are many attractions in the Central Valley. It is famous for its orchards and vineyards as well as some of California's finest museums and galleries. Refer to Central Valley's tourism website to plan one's trip.

There are a number of wine trails to consider following, so see some of the most stunning of the wineries in the region. One wine trail is the Madera Wine Trail in Madera Country.

The Madera is a unique grape-growing region where visitors can enjoy the local tasting rooms and discover the region.

Many people just skip the Central Valley in favor of the Coastal Ranges, the Sierra Nevadas, the Redwoods, or the coastal cities like LA and the Bay Area. But while all those regions in California are stunning, the Central Valley has many attractions of its own - particularly wineries.

The Fasi East Winery

There are far too many wineries (and even wine trails) to list off in California. But one winey on the Madera Wine Trail is the Fasi Estate Winery not far from Fresno. They are a small winery that focuses on quality and not quantity.

Their first vintage was in 2003, and since then, each vintage since has received Gold Medals, sometimes even reaching the “Best of Class” acclamation, proving the crucial point that Madera can compete with fine wines from any locale.

  • Address: 42415 Road 208, Friant

Tasting Room Hours:

  • Open Daily: 11:00 a.m. – 5:00 p.m. | $10.00 tasting fee, waived with two bottles minimum purchase

Other Prehistoric Waterways In The United States

At different times there were different waterways in the United States. The greatest of these was the Western Interior Seaway during the times of the dinosaurs. Since then there have been a few prehistoric lakes in the country.

As the Ice Age came to an end and the Launtinide Ice Sheet melted, a massive lake larger than the Great Lakes combined formed near the Great Lakes. That lake is called Lake Agassiz, and it existed between 30,000 and 10,000 years ago - so was probably still there when the first people moved into North America. Today travelers can find the remains and deposits of this lake all through the region, including Wisconsin.

Pyramid Rock in Pyramid Lake near Reno, Nevada
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Pyramid Rock in Pyramid Lake near Reno, Nevada

Another giant ancient lake was in what is today Nevada Lake Lahontan. Visitors can see the remains of ancient Native American settlements that were once dotting its shores as they would hunt the animals that would come to drink and feed in the vegetation of the lake. The ancient shorelines are also very visible in the rocks of the cliffs around Reno. Remnants of this lake include the stunning Pyramid Lake in Nevada just north of Reno.