Hogback Mountain, a shield volcano north of Goat Rocks and south of White Pass, was identified by Siebert et al. (2010) as a satellite vent of Goat Rocks. Rising in elevation, it erupted more than of olivine basalt and basaltic andesite from the end of the Pliocene through the early Pleistocene. Eruptions from Goat Rocks formed a spread-out volcanic field populated by small lava domes to the north, with dimensions of by .