There aren’t any volcanoes near Fresno. But you can hike up to an ancient lava bed | Opinion
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Unlike other regions of California, the San Joaquin Valley doesn’t have volcanoes.
However, there are telltale signs of prehistoric volcanic activity. Provided one knows where to look.
The most obvious example in Fresno and Madera counties is the series of flat tabletop-like mesas perched 1,000 feet above the Valley floor overlooking the San Joaquin River drainage. Of these mesas, Big Table Mountain is the most prominent and best known.
Geologists believe these basalt-lined table tops are the remains of ancient lava flow from a volcano that erupted 10 to 12 million years ago in what today is either eastern California or western Nevada. (The Sierra Nevada range, whose uplift occurred between 3 and 5 million years ago, is youthful by comparison.)
Opinion
The volcano produced enough lava to fill the ancestral San Joaquin River canyon, coating granite in the river channel with basalt flow that protected it from natural weathering. Over the ensuing millennia, the Sierra Nevada tilted upward to create the surrounding foothills while softer rock around the ancient river eroded – leaving the lava-coated bed elevated and exposed to the landscape.
It’s the classic geological tale of how a river bottom became a mountain top.
First-time visitors are often surprised to discover these table tops aren’t as flat as they appear from below. They’re actually quite lumpy and covered in rocks. Recharged by spring rains, vernal pools form in some places to provide temporary homes for fairy shrimp along with dozens of other rare plant and animal species under federal protection.
During the spring, these vernal pools are surrounded by bands of wildflowers with white and yellow petals called California meadowfoam. Which provides a striking foreground to views of the San Joaquin River as it winds toward Millerton Lake and, in the opposite direction, the western slope of the Sierra.
Most of the table tops are under some form of protection. Big Table Mountain and the neighboring McKenzie Table are the centerpieces of the 2,960-acre McKenzie Table Mountain Preserve, which is owned and managed by the Sierra Foothill Conservancy. The nonprofit offers regular hikes and classes on several preserves, including the McKenzie, and maintains a calendar of events.
The only table top accessible to the general public lies within the Big Table Mountain Ecological Reserve, a 1,000-acre managed by the California Department of Fish and Wildlife that borders the Millerton Lake State Recreation Area.
Getting there requires a 7.5-mile roundtrip hike from a small parking area at the gated end of Wellbarn Road, which typically fills up by mid morning on weekends with mild spring weather. The trail is easy to follow – it’s a dirt road – but not well marked. You basically follow the road down the hill, then take the left fork at the first obvious junction. After that it’s a steep, stiff climb to the top passing through two more gates.
Once you’re up there, there are several picnic tables to enjoy lunch, take in the panoramic views and marvel how a volcanic eruption hundreds of miles away and twice as old as the Sierra could produce such a landscape.
