During the Spring of 1790, a Spanish explorer, Captain Louis A. Arguello discovered a new river, on which floated a large number of feathers, apparently resulting from the intervention of a coyote or fox into a cluster of the many ducks that covered parts of the river upstream. He named the river, "Rio de las Plumas," which translates into the current name, "Feather River". The area didn't get a lot of attention again until about 1846, when Peter Lassen opened the Lassen Route to California, which went through the area. In 1849 and 1850, gold fever struck California, and many settlements were established along the Feather River.
In 1850, the California legislature established Butte County, which then included what is now known as Plumas County. Plumas County (named for the Spanish word for feathers) was established on March 18, 1954, when the population increased enough to draw the attention of the legislature.
A lot of the local towns and landmarks take their names from their founders; Greenville for the Green family that built the first house there and started a small motel, Prattville for Dr. Williard Pratt who retired there from his practice in Chico and built a hotel, Mt. Lassen for Peter Lassen, etc.. I have to note that I just came across some instructions calling for boiling water in German, and the German word for boil is Lassen, very appropriate for one of the two volcanoes that have erupted in the United States during the past century. The mountain continues to boil today.
In 1910, the Great Western Power Company started construction on a dam at the lower part of what was then known as Big Meadows. The original dam was abandoned and replaced with a larger earth-filled dam . When it was filled, it was named for the three daughters of Guy S. Earl, a vice president with the power company. Almanor came from "ALice", "MArtha", and "EliNORe", with the person naming it not realizing that Guy's daughter Elinore had an "e" on the end of her name.
The lake started off small, with only a few hundred thousand acre feet of water. Today, it usually reaches a peak of about 1.1 million acre feet, with a low point usually over 600,000 acre feet. It is part of one of California's largest hydroelectric systems, so its level is subject not only to the snowpack and rainfall, but also to the state's power needs. It is a major recreational asset for the people that live and visit in the area, with a wide and growing variety of summer and winter sports.