Oroville sits at the seam where the Sacramento Valley floor gives way to the Sierra foothills, and yards here reflect that split personality. Down along the Feather River and out through Thermalito, the ground is loose sandy loam left behind by gold dredging and river deposits, so water and nutrients drain away fast and mulch becomes less of a decoration than a necessity. Climb toward Oroville East, Palermo, or the pine country around Magalia and the slopes get steeper, the rock gets closer to the surface, and crushed stone or decomposed granite usually beats bark on a grade. With Zone 9b summers pushing past 100 degrees and only about 27 inches of winter rain to carry a landscape through, depth and material choice matter more here than in the flat orchard ground near Gridley or Durham.