The effect of an underlying magma reservoir cannot be identified within the complex gravity pattern in the Coso Range, California. Rather, linear gravity contours, which suggest a regional tectonic origin, enclose the location of most of the volcanic activity of the Coso Range. Faults along the edges of northwest trending, magnetic blocks probably provided paths of minimum resistance to the ascending viscous magma that was extruded as rhyolite domes. Dense, magnetic rocks associated with a complex mafic pluton 9 km in diameter form a relatively impermeable north border of the Pleistocene volcanic field. A heat flow high nearly coincides with the west half of a 6-km-diameter magnetic low. A 2-km-diameter outcrop of a pre-Cenozoic silicic pluton, which has low magnetization compared to the surrounding metamorphic rocks, presumably typifies the rocks that underlie the magnetic low and heat flow high. Hydrothermal fluids may have destroyed some magnetite in the more magnetic wall rock, further reducing the magnetic intensity.