You can get pretty isolated in the Kofa. The farther you get from the highway, and the farther you get off of the main roads, the fewer people you'll see. Nearer to pavement (and where people park their giant RVs) you'll get more side by side traffic (dust and noise can be a bummer in camp, at least for my curmudgeonly self). Farther away, I've had trips where we had nobody come by camp in two or three days.
But, I'll add that if one really values isolation, I like empty places on the map with no named human attractants. We've got lots of public land in our state like that.