Within park boundaries exists the nation's largest glacial system, with glaciers covering 35 percent of the parklands. Some glaciers do not look pristine like you might picture them. Those brown lines you see in the photo are medial moraines. According to the National Park Service:

Medial moraines form where two tributary glaciers come together. They are generally surficial features on the ice and often consist of rock that has fallen from a rockwall where the glaciers converge. Because they are thin, surficial features, medial moraines are rarely preserved after the ice retreats.