Yosemite Falls stands as one of the world’s tallest waterfalls, a dramatic cascade plunging over the sheer granite wall of the Sierra Nevada. The source of this immense volume of water is Yosemite Creek, a modest stream that begins high on the plateau above Yosemite Valley. The flow is a direct reflection of the mountain environment it drains, dictated by climate and geology. Understanding the falls requires looking into the specific geography and history of its path.
The Geography of Yosemite Creek’s Headwaters
The water that feeds Yosemite Falls begins in a remote, high-elevation area on the western slope of the Sierra Nevada. The headwaters are located at the Grant Lakes, a collection of alpine bodies of water situated on the plateau north of Yosemite Valley. This area forms the Yosemite Creek watershed, a small drainage basin covering approximately 43 square miles. The limited size of this watershed is a defining characteristic of the falls’ hydrology. The basin is composed primarily of granite, which resists erosion and does not hold water well. Glaciers scraped the surface clean, leaving behind thin soil and exposed rock. Because the granite basin lacks deep soil layers or large permanent reservoirs, water quickly drains from the high country and rushes into Yosemite Creek.
The Annual Cycle of Flow
The seasonal rhythm of Yosemite Falls is dictated by the annual accumulation and subsequent melting of the Sierra Nevada snowpack. The entire water supply is a product of this winter snow, which acts as a natural, frozen reservoir storing precipitation until spring. This reliance on snowmelt explains the dramatic variation in the falls’ appearance throughout the year. The flow typically begins to build in late fall, but the true surge starts in the spring. As temperatures rise in April and May, the snowpack melts rapidly, leading to a massive increase in water volume.
The falls reach their peak flow, or the “spring pulse,” during late May or early June, when the cascade can flow at rates of up to 2,400 gallons per second. This torrent gradually slows as the warmer summer months deplete the remaining snow. By mid-summer, the flow is significantly reduced, becoming a more gentle, segmented cascade. The falls frequently slow to a trickle, or even dry up completely, by late August or early September. The cycle is reset with the arrival of the next significant storm system in the late fall.
The Glacial History Shaping the Falls
The dramatic vertical drop of Yosemite Falls is a direct result of differential glacial erosion over millions of years. This geological history explains why the water drops from such a height at this specific location. Yosemite Valley was carved by a massive trunk glacier, the Merced Glacier, during the Pleistocene Ice Age. This main glacier was powerful, grinding and scouring the valley floor deeper and wider, creating the characteristic U-shaped cross-section.
Yosemite Creek flowed through a smaller tributary valley that contained a less powerful glacier. This smaller glacier was unable to erode its valley as quickly or as deeply as the main Merced Glacier. When the glaciers receded, the tributary valley of Yosemite Creek was left suspended high above the main valley floor, a feature known as a “hanging valley.” Yosemite Creek now plunges over the sheer cliff face created by this difference in erosion, dropping 2,425 feet in three distinct sections.