Lassen National Forest is a United States national forest of 1,700 square miles (4,300 km2) in northeastern California. It is named after pioneer Peter Lassen, who mined, ranched and promoted the area to emigrant parties in the 1850s.

Peter Lassen, later known in Spanish as Don Pedro Lassen, was a Danish-born Californian ranchero and gold prospector. Born in Denmark, Lassen immigrated at age 30 to Massachusetts, before eventually moving to California. In California, Lassen became a Mexican citizen and received the vast Rancho Bosquejo from Governor Manuel Micheltorena. He is best known as the eponym of Lassen County, California, Lassen Peak, and Lassen Volcanic National Park.