Crystal Peak is a mountain in the Diamond Mountains of the northern Sierra Nevada on the border of Lassen and Plumas counties, California. It lies about 36 miles in a straight line from another Crystal Peak in neighboring Sierra County, a nearby namesake sometimes regarded as its sister mountain. The peak takes its name from an unusual summit block that looks like solid quartz. Rising about forty feet above an otherwise flat summit, this block gives Crystal Peak its most distinctive character and explains the mountain’s name.