Zion winters are mild, and heavy snows don't usually reach the bottom of the canyon. Daytime temperatures can frequently hit 60°F; nights are often in the 20s and 30s.
A south-facing Trombe wall, seen in this 180° image as the lower two rows of windowpanes, provides most of the heating for the Visitor Center. Heat from the sun is trapped between a pane of glass and a black selective coating. A masonry wall stores heat for release into the building later in the day. Winter surface temperatures of the inside of the Trombe wall often reach 100°F (38°C).
Because the sun is high during the summer, roof overhangs help keep the building cool by blocking the wall from the sun. During the winter when the sun is low, it can shine under the overhangs and into the building to provide solar heat. The length and position of the overhangs were determined based on the Zion Canyon latitude and weather patterns.
More information on Trombe walls.