ZION A Geologic and Geographic Sketch of Zion National Park

A GEOLOGIC AND GEOGRAPHIC SKETCH OF ZION NATIONAL PARK

CLIMATE—VEGETATION—ANIMALS

In Zion National Park the annual rainfall ranges from 10 to 20 inches and the temperature from 10° to 105°. The winters are short and mild; the summers long and hot. Though varying greatly from year to year, month to month, and even day to day, the precipitation is so distributed as to produce two wet cycles, one in winter and early spring and one in late summer, and two dry cycles, one in late spring and early summer and one in late fall. In response to these conditions many species of plants complete their life cycle before June, and other begin their cycle in late summer and complete it in the fall. Beginning early in May the spring cycle is the time for violets, orchids, pentstemons, sego lily, and in shady nooks the columbine and monkey flower. During the excessive heat of summer day-blooming plants are largely replaced by such night-blooming species as evening primrose, four o'clock, spiderwort, and the glorious sacred datura—a veritable "moonlight garden." During the late summer cycle the roads pass through fields of asters, sunflowers, bee flowers, Indian paint brush, and sweet clover, and the cool shady nooks are made brilliant by the cardinal flower. There is little evidence of any zonal distribution of plants based on latitude or the equivalent altitude. The range in kinds of soil, exposure to the sun, and amount of ground water is so great that indigenous plants of the Lower Sonoran, Upper Sonoran, Transition, and even Canadian zones, together with most migrating plants, find favorable habitats. On the floor of the canyon are groves of boxelder, willow, cottonwood, and ash. Above them on the talus slopes and here and there in cracks on the towering walls grow juniper, pinon, live oak, and manzanita—stunted trees and shrubs characteristic of semiarid regions. On the Kolob Terrace above the canyon walls, at an altitude of about 7,000 feet, yellow pine, white fir, Douglas fir, and aspens are the dominant species. But in favorable places these pines and firs extend to the floor of the canyon, 3,000 feet below; yuccas grow high on the rim, and in damp niches are ferns and other plants that normally prefer much colder climates. On Horse Pasture Plateau pinons and junipers characteristic of the Upper Sonoran zone grow on sunny slopes at 7,300 feet, and 1,000 feet below them, in a shady valley, are yellow pines and quaking aspens of the Transition zone.

The distribution of animal life in Zion National Park is indeed varied, for the deep narrow shaded canyons and open sunny slopes have provided habitats for animals of Sonoran, Transition and Canadian zones. Thus it seems that the desert and the plateau have been telescoped together as far as many forms of animal life are concerned. Of the approximately 150 species of birds recorded from the park there are such forms as the road-runner, water ouzel, shrike, phoebe, titmouse, kinglet, kingfisher, burrowing owl, golden eagle, Gambel's quail, Treganza's heron, warblers, hummingbirds, vireos, kingbirds, and many flycatchers. The mammals present a mixed group with such forms as deer, cougar, porcupine, ringtail cat, water shrew, antelope ground squirrel, rock squirrel, skunk, gray fox, meadow mouse, kangaroo rat, pocket gopher, and rabbits. Perhaps the forms least expected to be found in the park are the reptiles and amphibians. Among the reptiles there are the following lizards:—chuckwalla, leopard lizard, collared lizard, sonoran whiptail, desert scaly lizard, cliff uta, and Skilton's skink. Then there are the snakes:—great basin rattlesnake, gopher snake, Boyles king snake, garter snake, thimble snake, bi-colored ground snake, spotted night snake, and the rare patch-nose snake. Amphibians recorded from the park as are follows:—tiger salamander, leopard frog, desert tree-toad, spadefoot toad, rocky mountain toad, and canyon toad. Invertebrate forms are likewise varied and abundant, but perhaps the most noted invertebrate is the Zion snail (Petrophysa zionis) which lives only on the wet walls of nearly sheer cliffs along the Narrows of the Virgin River.