By the Pliocene epoch, radially directed alpine glaciers had eroded away much of the bimodal stratovolcano cap, leaving behind a series of U-shaped valleys with intervening ridges that comprise the Level Mountain Range. This dissection of the bimodal stratovolcano was followed by the felsic dome-forming stage. Eruptions of felsic magma were predominantly viscous during this stage of activity, resulting in the magma piling up thick around volcanic vents to create a series of lava domes. Individual domes grew up to in the glacially eroded core of the bimodal stratovolcano.