Changing Shorelines of Clear Lake
The shape of Clear Lake changed several times over the last half million years leaving behind uplifted areas and fertile alluvial soils. Tectonic events including the formation of Mt Konocti, changing drainage outlets for the Lake and a landslide on Cow Mountain impacted the shoreline of Clear Lake, creating the soils and topography that are Lake County today. Between 460,000 and 475,000 years ago, the Big Valley District was part of the lake bed of Clear Lake.
The deep fertile soils of the area were created in the lakebed environment when Clear Lake covered the Big Valley. The topography of this area is a flat basin surrounded on three sides by uplifted terraces that rise to mountainous terrains and Clear Lake on the fourth side. This topography accounts for the winds and air movement, and rainfall in the area. The southern portion of the proposed Upper Lake Valley area was also once part of the lake bed of Clear Lake.
The lakebed covered a portion of the proposed area for an estimated 250,000 years. During this period, Clear Lake drained northwest through Cold Creek Canyon into the Russian River basin. Sometime in the last 10,000 years, a landslide on Cow Mountain blocked the Cold Creek Canyon. Over time, with the rise in the level of the lake, Clear Lake carved a new outflow into the Sacramento River watershed and the lakebed receded to its present day structure.
History of Clear Lake
The Clear Lake Basin was shaped by a variety of processes over the last 1 to 2 million years. Scientists have recovered a nearly continuous sequence of lake sediments dating back 475,000. Other lake sediments in the region that date back to the Early Pleistocene, approximately 1.6-1.8 million years ago. Read more…