What geological feature is primarily responsible for the Grand Canyon's depth and width?

The erosive action of the Colorado River is the primary geological feature responsible for the Grand Canyon's remarkable depth and width. Over millions of years, the river has carved its way through layers of rock, effectively deepening and widening the canyon. The sustained flow of water, combined with natural wear from sediment and debris carried by the river, has created the stunning geological landscape we see today.

While volcanic activity, tectonic movements, and sediment accumulation play roles in the broader geological context of the region, they do not directly account for the specific formation of the Grand Canyon. Volcanic activity may influence nearby landscapes, but it does not primarily shape the canyon itself. Tectonic movements can result in the uplift of the land, which provides an elevation from which the river can erode downward. Sediment accumulation can affect river paths and landscapes but is not a force that directly carves the deep valleys seen in the Grand Canyon.

Thus, the erosive power of the Colorado River is the key agent responsible for the canyon's iconic profile, making it the correct answer.