Geology

The Bear River's early geology story is as dramatic as its later human history. For this river's basin was invaded by its neighbor to the north, the Yuba River, and half the Bear watershed was stolen away and now flows down the South Yuba River. This strange, unusual tale is best told by just looking closely, for the rocks tell the story.

As you look at the panoramic picture of the Bear River (above), it is easy to imagine that the rain and snow falling high in the mountains flow down to the valley below, and continue downstream to the sea. But they don't.

The Source of the Bear River

Take another look. There is a big gap in the ridgetop in the middle of this photo, called the Yuba Gap. Natural erosion and waves of glaciers acted together to form this steep canyon gap through the ridge, dividing the Bear and the Yuba. The Yuba kept eroding this ridge from the north, and the relentless ice of the glaciers kept cutting deeper and deeper into this same slit until the headwaters of the Bear spilled through to the Yuba. All the water from the ancient Bear headwaters on the right of the photo actually flow through this canyon gap north to join the Yuba. The waters of today's Bear River now begin just above the meadows of the Bear Valley in the middle of the photo (picture at right shows the source of the river). The Bear River was one of the great rivers of the Sierra in ancient times, but today with its far smaller watershed, it is labeled a "subwatershed" by the State of California.

This aberration of nature also made it easy to divert these Yuba River waters back into the Bear River, since instead of having to go through the mountains and ridgetops that normally separate rivers, all the miners had to do was build a canal over the tiny hill that now separated the Yuba from the Bear. And build canals they did. The waters of the Middle Yuba are now diverted to the South Yuba to the Bear River, and finally end up in the American River's Rattlesnake Bar at Folsom Reservoir.

Read more about the Bear River's geomorphology (PDF*, 99 KB) …