The flood of 1861/1862 put much of the Central Valley under water. But a few years later, a dramatic and unusual event resulted in an even bigger flood in Visalia. The story of the Dennison Mountain landslide, today on KVPR’s Central Valley Roots.
Dennison Mountain is a remote peak in Sequoia National Park .At around 8,600 feet, the mountain marks the divide between the Kaweah and Tule River watersheds. But in 1867, it was the site of an important geologic event.
In December of that year California was pummeled with intense storms. Then on December 20th, 1867, a rare event happened. The north side of the mountain gave way, sending a rockfall downslope of massive proportions. The rocks and debris destroyed much of the Garfield Grove of giant Sequoias, before creating a natural dam that measured 400 feet high and a half mile across. It was enough to back up a portion of the South Fork of the Kaweah River, creating a lake.
About 1 day later, the rockfall dam gave way, sending a torrent of water down the Kaweah River. Some accounts say it was as much as 40 feet high. When the waters reached Visalia, the town was under 5 to 6 feet of water. Geologists now say that there is evidence of similar slides and floods across the Kaweah River watershed.
