The existence of igneous dikes beneath grabens in Tharsis remains contentious due to conflicting observations of Martian geomorphology. We examine the topographic signatures of a Tharsis-radial graben array in 3 zones south of Arsia Mons. We identify dikes beneath grabens in all of the zones, with fewer dike-induced grabens closer to Arsia Mons. We infer that a single radial swarm of dikes outside the magmatic source area, central Tharsis, is unlikely. Our observations instead favor a long and varied magmatic history throughout Tharsis with several episodes of dike injection.