Carnelian Bay is an unincorporated community on the shore of Lake Tahoe in Placer County, California, United States. The Cornelian Bay post office operated from 1883 to 1887 and from 1891 to 1893. The Carnelian Bay post office opened in 1908. For statistical purposes, the United States Census Bureau has defined Carnelian Bay as a census-designated place. The census definition of the area may not precisely correspond to local understanding of the area with the same name.