When Spanish explorers in the 16th century first encountered the Baja California Peninsula, west of the Sea of Cortez, they believed the peninsula to be an island similar to the island described in de Montalvo's novel. They named the land California. Initially, California applied only to Baja California Peninsula, but as Spanish explorers and colonizers moved north and inland, the region known as California, or Las Californias, grew. Eventually it included not only the peninsula, but also the lands north of the peninsula including what is now the U.S. states of California, Nevada and Utah, as well as parts of U.S. States of Arizona, Colorado, New Mexico and Wyoming. After Mexico's independence from Spain, the upper territory became the Alta California province, and the lower territory became Baja California.