The Warner Mountains are an 85-mile -long mountain range running north–south through northeastern California and extending into southern Oregon in the United States. The range lies within the northwestern corner of the Basin and Range Province, extending from the northeastern corner of Lassen County, California, through eastern Modoc County, Califor…The Warner Mountains are an 85-mile -long mountain range running north–south through northeastern California and extending into southern Oregon in the United States. The range lies within the northwestern corner of the Basin and Range Province, extending from the northeastern corner of Lassen County, California, through eastern Modoc County, California, and northward into Lake County, Oregon.