The term "Inland Empire" is documented to have been used by the Riverside Enterprise newspaper (now The Press-Enterprise) as early as April 1914. Developers in the area likely introduced the term to promote the region and to highlight the area's unique features. The "Inland" part of the name is derived from the region's location, about 60 miles (97 km) inland from Los Angeles and the Pacific Ocean. Originally, this area was called the Orange Empire due to the acres of citrus groves that once extended from Pasadena to Redlands during the first half of the 20th century. The Inland Empire is a nebulous region, but is defined as the cities of western Riverside County and the cities of southwestern San Bernardino County; adjacent to the Los Angeles metropolitan area. A generally broader definition will include the desert community of Palm Springs and its surrounding area, and a much larger definition will include all of San Bernardino and Riverside counties.
What is now known as the Inland Empire was inhabited for thousands of years, prior to the late eighteenth century, by the Tongva, Serrano, and Cahuilla Native Americans. With Spanish colonization and the subsequent Mexican era the area was sparsely populated at the land grant Ranchos, considering it unsuitable for missions. The first American settlers arrived over the Cajon Pass in 1851, a group of Mormon pioneers who were the first residents of San Bernardino. Although the Mormons left a scant six years later, recalled to Salt Lake City by Brigham Young during the church's Utah War with the US government, other settlers soon followed.
The entire landmass of Southern California was subdivided according to the San Bernardino Meridian, which was first plotted as part of the Public Land Survey System in November 1852, by Col. Henry Washington. Base Line road, a major thoroughfare, today runs from Highland to San Dimas, intermittently along the absolute baseline coordinates plotted by Col. Washington. San Bernardino County was first formed out of parts of Los Angeles County on April 26, 1853. While the partition once included what is today most of Riverside County, the region is not as monolithic as it may sound. Rivalries between Colton, Redlands, Riverside and San Bernardino over the location of the county seat in the 1890s caused each of them to form their own civic communities, each with their own newspapers. On August 14, 1893 the Senate allowed Riverside County to form out of land previously in San Bernardino and San Diego counties, after rejecting a bill for Pomona to split from L.A. County and become the seat of what would have been called San Antonio County.
The arrival of rail and the importation of navel and Valencia orange trees in the 1870s touched off explosive growth, with the area quickly becoming a major center for citrus production. This agricultural boom continued with the arrival of water from the Colorado River and the rapid growth of Los Angeles in the early 20th century, with dairy farming becoming another staple industry. In 1926, Route 66 (now known as Foothill Boulevard and Interstate 215) came through the northern parts of the area, bringing a stream of tourists and migrants to the region. Still, the region endured as the key part of the Southern California "Citrus belt" until the end of World War II, when a new generation of real-estate developers bulldozed acres of agricultural land to build suburbs. The precursor to the San Bernardino Freeway, the Ramona Expressway, was built in 1944, and further development of the freeway system facilitated the expansion of suburbs and human migration throughout the Inland Empire and Southern California.
The region experienced significant economic and population growth through most of the latter half of the 20th century. In the early 1990s, the loss of the region's military bases and reduction of nearby defense industries due to the end of the Cold War lead to a local economic downturn. The region as a whole had partially recovered from this downturn by the start of the 21st century through the development of warehousing, shipping, logistics and retail industries, primarily centered around Ontario. However, these industries have been heavily affected by the Great Recession.
Physical boundaries between Los Angeles and the Inland Empire from west to east are the San Jose Hills splitting the San Gabriel Valley from the Pomona Valley, leading to the urban populations centered in the San Bernardino Valley. From the south to north, the Santa Ana Mountains physically divide Orange County from San Bernardino and Riverside Counties. The Santa Rosa Mountains, as well as the Southern California portion of the Sonoran Desert, physically divide Riverside County from San Diego County. Some definitions for the I.E. consist of the Chino Valley, Coachella Valley, Cucamonga Valley, Menifee Valley, Murrieta Valley, Perris Valley, Temecula Valley, and Victor Valley.
Elevations range from 11,499 ft (3,505 m) at the top of the San Gorgonio Mountain to -220 ft (-67 m) at the Salton Sea. The San Bernardino mountains are home to the San Bernardino National Forest and the resort communities of Big Bear Lake, Lake Arrowhead, and Running Springs. The Santa Ana River extends from Mt. San Gorgonio for nearly 100 miles (160 km) through San Bernardino, Riverside, and Orange counties before it eventually spills into the Pacific Ocean at Newport Beach and Huntington Beach. While temperatures are generally cool to cold in the mountains, it can get hot in the valleys. In the desert resort of Palm Springs, near Joshua Tree National Park, summer temperatures can reach well over 110 °F (43 °C).
Unlike most metropolitan areas that have grown up around a central city, the Inland Empire has no one main focus city. Major cities in the region include Riverside, San Bernardino, Rancho Cucamonga, and Ontario. Suburban sprawl spreads out to form a unified/built up connection with the Los Angeles metropolitan area. Further development is steadily, if not heavily, encroaching past the mountains into the outlying desert areas. The Inland Empire borders both Los Angeles and Orange counties. Freeways in Southern California are heavily used, but this comprehensive freeway system has made travel between the Inland Empire and these two counties generally easy; especially to and from Los Angeles County.