The Pacific Crest Trail is one of the great long-distance walking routes in North America, stretching from the US-Mexico border in southern California to Manning Provincial Park in British Columbia. Its official southern terminus is near Campo, just north of the international boundary fence. A simple monument marks the spot.

For hikers attempting the full trail — or even just the first hundred miles through the hot, dry mountains of San Diego County's backcountry — Campo is the starting point. In April each year, when thru-hiking season begins, small clusters of backpackers appear at the terminus and begin walking north through desert terrain toward the Sierra Nevada, Oregon, Washington, and eventually Canada. They resupply in towns along the way. They walk for months. It all begins in this quiet corner of San Diego County.

The town of Campo grew up alongside railroad infrastructure. The former Southern Pacific line — originally the San Diego and Arizona Railway — ran through here, connecting the backcountry to the coast. The railway's Campo Depot became a local landmark. Freight operations on the successor Carrizo Gorge Railway have been embargoed, but the Pacific Southwest Railway Museum at 750 Depot Street operates passenger service and preserves the history of railroading in the region.

Before the railroad there was a stagecoach. In 1869, John Capron established a regular run from San Diego through Dulzura and Campo to Yuma, which operated until 1912. The stagecoach brought commerce, the commerce brought crime, and the crime brought the Army — a sequence that eventually gave rise to Camp Lockett, the cavalry post whose grounds now partly serve as a juvenile detention facility.

Campo sits close to the Mexican border, and the border defines much of the town's economic reality. The US Department of Homeland Security Border Patrol is one of the largest employers in the area, along with the San Diego County Probation Department's Juvenile Ranch Facility, which houses approximately 250 residents. The Campo Band of Mission Indians maintains a reservation about 1.5 miles north of town.

The 2020 census counted 2,955 people in Campo, spread across a landscape where the population density is 125 people per square mile — low enough that open land defines the place more than any built environment. The median age was 39. Hispanic or Latino residents made up 36.8 percent of the population.

There is a private airstrip near the intersection of Lake Morena Drive and Hauser Creek Road — about 0.6 miles long, unnamed, not in federal air traffic databases — that summarizes something about Campo's relationship to infrastructure. Things get built here to serve immediate needs, often without being formally registered or widely announced.

Campo is in San Diego County, technically, but it is a long drive east from the coast on State Route 94. The mountains between here and the suburbs are the mountains that the Pacific Crest Trail crosses in its first hard days. The heat in summer is real. The isolation is real. And the border, a mile to the south, is the reason that most of the institutions in this town exist at all — the cavalry posts of the nineteenth century, the World War II base, the current Border Patrol presence. Campo is a place that the border made.