On the Distribution of Utah's Hanging Gardens

Great Basin Naturalist Volume 49 Number 1 Article 1 1-31-1989 On the distribution of Utah's hanging gardens Stanley L. Welsh Brigham Young University Follow this and additional works at: https://scholarsarchive.byu.edu/gbn Recommended Citation Welsh, Stanley L. (1989) "On the distribution of Utah's hanging gardens," Great Basin Naturalist: Vol. 49 : No. 1 , Article 1. Available at: https://scholarsarchive.byu.edu/gbn/vol49/iss1/1 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. The Great Basin Naturalist Published at Provo, Utah, by Brigham Young University ISSN 0017-3614 Volume 49 31 January 1989 No. 1 ON THE DISTRIBUTION OF UTAH'S HANGING GARDENS Stanley L. Welsh 1 Abstract. —This is a summary monograph of the hanging gardens as they occur in the Colorado River and Virgin River portions of the Colorado Plateau in Utah. Discussed in this paper are the hanging gardens, their geography, geomorphology, aspects of distribution and diversity, and principal vascular and algal plant species. Animal trapping studies and plant productivity aspects are reviewed. The sea of aridity that overlies southern tively recent origin, geologically speaking Utah and vicinity is broken by seasonal influ- (Hintze 1972). ences and by the dendritic trenches of the The geological strata are remarkably evi- Colorado River and its tributaries. The effects dent in this arid setting, where vegetative of the river are restricted to its banks and cover is thin and where rate of soil develop- adjacent alluvial terraces; the riparian vegeta- ment is exceeded by processes of erosion. No tion is generally both monotonous and pre- great bodies of contemporary alluvium serve dictable. Away from the riverbanks aridity is to obscure the underlying geology as in the the general rule. However, here and there on Great Basin to the west. The Colorado River the canyon walls are moist places clothed in and its tributaries have excavated the allu- green. They are well-watered islands in an vium almost as it has formed. The canyon is ocean of drought (Figs. 1 and 2). It is with open to the south, and the products of erosion these patches of greenery that this paper is have been transported in the great river. Ped- involved. They must be placed within their iments of ancient erosional deposits persist for setting in order to understand the contrast of a while perched atop highlands between arms their mesophytic vegetation with the xeric of modern drainages, but raw geological strata communities that surround them. are exposed over huge areas of the basins of The Colorado River system is entrenched the Colorado. into a great platform supported by a geological Reason for the sparse protective layer of substructure more than a billion years old. plants and for the limited soil development Impressive as the inner gorges of this canyon are related to the general aridity of the region. are, the broader aspect of the system is evi- The dryness is a function of both low precipi- dent to the east or south of the Wasatch tation and high evaporation. Eubank (1979) Plateau in central Utah. The canyon of the records the following long-time precipitation Colorado at that point is more than a hundred means (in inches, followed by centimeters miles wide, having yielded to the processes of in parentheses) for the following stations: erosion hundreds of cubic miles of alluvium. Hanksville 5.19 (13.18), Green River 6.06 Despite its huge size, the canyon is of rela- (15.39), St. George 8.78 (22.3), Moab 8.82 Life Science Museum and Department of Botany and Range Science, Brigham Young University, Provo, Utah 84602. Great Basin Naturalist Vol. 49, No. 1 (22.4), Price 9.88 (25.1), Blanding 13.21 (33.55), and Zion National Park 14.61 (37.11). Mean temperatures Fahrenheit (centigrade in parentheses) for those stations are: Zion National Park 61.2 (16.2), St. George 60.1 (15.6), Moab 55.0 (12.8), Hanksville 52.3 (11.3), Green River 52.5 (11.2), Blanding 49.4 (9.7), and Price 48.8 (9.3). Extreme temperatures are probably more important than means to the survival of plants. Summer temperatures greater than 100 degrees Fahren- heit (38 degrees centigrade) are common at all of the selected stations, and winter temperatures of below zero on that scale have been recorded at all stations. My first experience with this grandly arid country occurred almost four decades ago when I visited Glen Canyon and the townsite of Hite. I was traveling as a student in a class led by Professor Bertrand F. Harrison. No measurable rain had fallen for more than a year at the pioneer community, along the Col- orado River at the mouth of Trachyte Wash, Fig. 1. Map of Utah showing distribution of hanging gardens discussed in this paper. that 17th of May 1950 when I visited there. Fig. 2. Ribbon Garden, Ribbon Canyon, Lake Powell, San Juan Co., Utah. Sparingly vegetated Navajo Sandstone is cut by Glen Canyon, Ribbon Canyon, and Cottonwood Canyon. January 1989 Welsh: Utah's Hanging Gardens Table 1. Geological strata and distributions of hanging ment, whether alcove, terrace, or window- gardens. blind (Welsh and Toft 1981), is determined by the nature of geological Geologic age Strata Region the formation and the presence or absence of joint systems. Com- Cretaceous Wahweap Kaiparowits plexity of the plant Straight Cliffs Kaiparowits community within a hang- Jurassic Morrison Bluff ing garden is a function of quantity and quality (Bluff Sst) of water, developmental aspects, and accessi- Entrada (various Arches bility of plant species to it. members) Kaiparowits Hanging gardens occur in sandstone forma- Lake Powell Navajo Sandstone Canyonlands tions and sandstone members of several for- Lake Powell mations ranging in age from Pennsylvanian to Zion Canyon Cretaceous. Massive sandstones seem to be Triassic Navajo Sandstone Canyonlands best suited for alcove development coinciden- Zion Canyon Kaventa Lake Powell tal with garden formation, some better than St. George others. The formations with greatest develop- Zion Canyon ment are the Navajo and Entrada, both of Moenave Zion Canvon them cross-bedded, massive formations com- (Springdale Sst) posed of wind-blown sand and containing an- Chinle (Shinarump Egl) Zion Canyon cient pond bottoms that serve as impervious Permian White Rim Canyonlands bedding planes. The Wingate Formation is of Cataract Canyon similar composition but lacks significant hang- Cedar Mesa Natural Bridges ing gardens. More thinly bedded sandstone Pennsylvanian Hermosa Cataract Canvon formations tend not to form alcove gardens similar to those of the Navajo or Entrada. occur, Despite the aridity, there had been sufficient Exceptions however. Main formations bearing hanging gardens are listed in Table 1. unmeasured water to allow for germination of Less than massive, though not especially some seeds, and a few diminutive plants of red bedded strata such as the Kayenta at St. brome had each matured a solitary seed, re- George, Springdale Sandstone at Zion, and placing those from which they had germi- the Bluff Sandstone at Bluff, are alcove form- nated. And, plants of datura displayed their ers. The base of the alcove is not in the sand- huge, sweetly scented white flowers, which stone formation, however. Instead, the base is contrasted with the red, barren background. on the impervious formation beneath the Princes plume grew against a backdrop of sandstone. purple siltstone, the difference in hue both The Colorado River is entrenched into geo- pleasing and startling. logical strata that are displayed over vast re- Later on that same trip to the canyon coun- gions in flat or only somewhat inclined posi- try of the Colorado, we reached Natural tions. The strata are those exposed in that Bridges National Monument, where we more or less stable geological highlands east of camped. The following day we explored Arm- the hingeline in Utah (Hintze 1972). The strong at the and White canyons, looked canyons dissected into those highlands dis- amazing bridges, and observed the small, ver- play vast sandstone surfaces along their walls. tical wet seeps, occupied by mesophytic The sands of formations suitable for hanging plants. This was my first introduction to the garden development were deposited mainly peculiar vegetative assemblages known as on land, as dunes with interdune valleys. The hanging gardens. At the time their peculiarity interdune valleys were often the sites of lakes, was lost in the immense amount of informa- whose bottoms were made impervious by ac- tion thrust upon a student in this remarkable cumulations of dust and other fine particles. land for the first time. Thin layers of limestone are evident in many The hanging gardens result from coinci- of the bedding planes. Turned to stone, the dence of water in perched bedding planes ancient lake and pond basins continue to exist within sandstone strata intersected by the within the strata. Water percolating through dendritic drainages of the Colorado River the porous rock encounters the ancient bed- system (Fig. 1). The kind of garden develop- ding planes, still impervious and capable of Great Basin Naturalist Vol. 49, No. 1 holding water. When filled to overflowing, winds. Thus, there is a diversity of gardens. these bedding planes carry the water down- They vary in size, aspect, exposure to the ward to the next bedding plane beneath or to elements, water quantity and quality, num- another impervious stratum at the base of the ber of bedding planes, and amount of light formation.

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