The Mojave Desert is a desert region that covers parts of the county, mainly in the Antelope Valley and the northwestern corner. It is characterized by arid climate and diverse flora and fauna.
The San Gabriel Mountains are a mountain range that runs along the northern and eastern edge of the county, from the Santa Clarita Valley to the San Bernardino County line. They are also part of the Transverse Ranges and contain the highest peak in the county, Mount San Antonio.
The Los Angeles Basin is a coastal plain that covers most of the central and southern parts of the county. It is bounded by the Santa Monica Mountains, the San Gabriel Mountains, and the Pacific Ocean. It is the most densely populated and urbanized area in the county.
The Pomona Valley is a valley in the eastern part of the county, between the San Gabriel Mountains and the Chino Hills. It is the location of the city of Pomona and several other cities and towns.
The Transverse Ranges are a series of mountain ranges that run east-west across the county and the state. They include the Santa Monica Mountains, the San Gabriel Mountains, the San Bernardino Mountains, and the Santa Ynez Mountains.