Table Mountain is composed of Table Mountain Latite, which formed from potassium-rich lavas erupted from a center of volcanism near modern-day Sonora Pass around 10.4 million years ago. The lava flows followed the course of the ancestral Stanislaus River, filling the river valley. As the Sierra Nevada Mountains were uplifted, the softer sediments surrounding the flows were eroded away, leaving behind an inverted river valley. Although the formation stretches for miles and rises hundreds feet above the surrounding landscape, its width rarely exceeds a few hundred feet. Most outcrops on Table Mountain reveal flow-top breccias, while some outcrops show distinctive columnar jointing.