Frémont then ordered his main party - which included Kern and Joseph Walker - to travel the southern Sierra route over the pass Walker had discovered a decade earlier, while Frémont and a few others crossed the northern Sierra at Donner Pass. Frémont named the pass through which Walker led the party Walker Pass. Kern mapped the Kern River, which at the time was known as the Rio de San Felipe, as named by the Spanish. Later, Frémont named the river after his artist. Kern's campsite in the Kern River Valley, at the junction of the South and North Forks of the Kern River, now lies submerged by Lake Isabella. A historical monument for Kern's site was placed above the reservoir near its eastern shore on Highway 178.