Both the East Fork and North Fork of the Virgin River run through Zion National Park, converging just south of the park. Zion Canyon, the most prominent geological feature, is a deep chasm with nearly vertical walls that were cut through Mesozoic sedimentary rocks by the North Fork as it meandered toward the desert floor 3,000 feet below. The canyon is so deep and narrow that sunlight rarely penetrates to the bottom. Here, climatic zones, determined by elevation, affect weathering and erosion as well as the distribution of plant and animal life. Zone boundaries are not sharply defined.
Wet seasons are usually in early spring and late summer.
Most of the scouring of the canyons is performed by spring floods or by flash floods during intense summer storms. Winters can be mild with daytime temperatures often reaching 40 degrees F. Spring and Fall are good times to visit the park when temperatures range from 45 degrees F. at night to 80 degrees F. during the day. The South Entrance is on Utah Route 9 about 60 miles south from Cedar City via I-15 and Utah Route 17.