The glaciers that filled the Sierra Nevadan valleys carved V-shapes into the rocks.

The statement highlights the geological process of glaciation, particularly in the Sierra Nevadan region. Glaciers, which are massive, slow-moving bodies of ice, have the ability to erode the landscape through processes such as plucking and abrasion. As they advance and retreat, they carve out deep, U-shaped valleys and steep, V-shaped troughs in the rock layers beneath them.

The V-shaped valleys formed by glaciers can be attributed to the way water flows during warmer months, where meltwater erodes the rock, deepening the valley. Over time, as glaciers continue to carve through the rock, they create distinct features in the landscape, which are evident today in the Sierra Nevada mountains.

Understanding the interaction between glaciers and geological formations helps to illustrate the dynamic nature of Earth's surface, showing how landforms evolve over geological time scales. Additionally, the presence of V-shaped valleys indicates past glacial activity, which is significant for studying climate change and the history of our planet's environments.