I live in Siskiyou County, California. At 6,347 square miles (over four million acres) it is the fifth-largest in the state. There were a mere 44,900 residents as of the last census, meaning about seven souls per square mile (or 90 acres per person). It ranges in elevation from about 500 feet above sea level in the Klamath River basin to over 14,000 feet at the top of Mt. Shasta. Rugged mountains, high valleys, maze-like canyons, and volcanic plateaus make up the bulk of the terrain. Coniferous forests are abundant and the US Forest Service owns most of the real estate. Ranches, farms, small towns, and isolated hamlets make up the rest. It’s a remote, lonely place with high desert, alpine, and even Mediterranean climates. And it is bisected by Interstate-5, the nation’s busiest highway.
Here’s a map from 1887: