Complex sentence: Eruptive activity continued at Old Snowy Mountain into the middle to late Pleistocene, yielding hornblende andesite lava flows that were subsequently glaciated in the Cispus River valley; whether Old Snowy Mountain is a vent of Goat Rocks or an independent volcano remains unclear.
Split into simpler sentences: Eruptive activity continued at Old Snowy Mountain into the middle to late Pleistocene, yielding hornblende andesite lava flows that were glaciated in the Cispus River valley. Whether Old Snowy Mountain is a vent of Goat Rocks or an independent volcano remains unclear.