The 1854 Gazetteer of the United States by Thomas Baldwin shows:

EL DORADO, a county towards the N. part of California, bordering on Utah territory, has an area of about 2000 square miles. It is bounded on the N. by the American river it is also drained by the S. fork of the American river, which forms the outlet of Bonpland lake, and by Carson's and Walker's rivers, which flow eastward into Utah territory. The surface is uneven, being traversed by the Sierra Nevada, or Snowy Range of California. The census of 1852 gives no returns for this county. It is, however, known to be one of the most populous in the state. The number of inhabitants is estimated in the governor's late message at 40,000. The name El Dorado is of Spanish origin, and signifies, "the golden," or, "the golden country." Capital, Culloma.