In the winter of 1933 and spring of 1934, an expedition, led by Frank Beckwith of Delta Utah, conducted a reconnaissance survey for the Department of the Interior to inventory and assay the natural and scientific resources found within and nearby the recently established Arches National Monument. Joeseph C. Anderson was engaged to study the geology of the monument and deliver a detailed report to officials at the Department of the Interior. The following is a transcript of the official report.

The Arches National Monument, consisting of three closely related areas, covering approximately 7500 acres of land is located in the south central part of Grand County, Utah.

Situated as it is in the disturbed area flanking the La Sal Mountains the National Monument is difficult to reach as only low-grade desert roads lead from the main highways into the vicinity, and from the ends of these long hikes or horseback trips are required to reach the attractions in the monument proper. For this reason very few people outside of the nearby settlements are acquainted. with the spectacular erosion forms to be seen, which consist of numerous sandstone arches, cliffs, pinnacles, vertical slabs and bad-land erosion. Moab which 12 the nearest town, and the County seat of Grand County lies about eight miles south.

The present investigation was begun in December 1933 and completed in April 1934, as a project, with appropriation from the Federal Civil Works Administration, and under the direction of the National Park Service through Zion National Park.

Instructions required reconnaissance investigation in Archaeology, topography and geology. For the purpose of this report the results of geologic reconnaissance only will be treated.

While there is no published work on the Arches, parts of the region have been covered by several different publications. The most recent reports on the area and those covering the immediate vicinity came as a result of the oil prospecting activity around Moab in recent years.

Geologic reconnaissance and mapping was conducted during parts of two eight week periods. Daring the first term of work, mapping was done by triangulation, with plane-table and telescopic alidade, from a measured base-line. Drainage and formation contacts were sketched from stations thus located. Work the second eight weeks was greatly facilitated by the aid of a rodman, when a long stadia traverse was run nI some detail mapped by stadia observations. since no bench mark was available in the area it Was necessary to assume a base-line elevation and carry vertical control from there on 1y vertical angles.

The topography varies radically over different parts of the area, each of the three divisions having distinct characteristics. The section known as The Arches is a northeast - southwest trending stringy; of narrow mesa rock lands dropping, off to steep cliffs on all sides, and the tops of the mesas are inaccessible because of the vertical walled cliffs which are in no place cut low enough for ascent. Around the cliff mesa lands are low rolling sandstone hills which on the north side break off and dip moderately toward the main drainage in that direction known as Salt Wash. (See Fig. 2)

Situated along the north rim of the Salt Valley Anticline (See Fig. 1) is the area known as The Devil's Garden, where the massive sandstones have been fractured and eroded into long rib-like slabs which stand closely spaced and at times alone in low sandy flats. These vertical slabs attain heights estimated at 350 feet.

The Yellow-Cat section presents an entirely different aspect. Here high buttes are weathered into typical badland forms. The greatest difference in elevation at this place amounts to more than 500 feet. (See Fig 3)

The vegetations is in keeping with the climate of the area which is arid. Black brush, junipers and the two-needle pinion represents the most abundant of the vegetation, though there are occasional chimps of cottonwood, scrub oak and willows where conditions are favorable. There is one characteristic and unique tree that deserves special consideration. In the summer it dots the landscape with patches of bright green -- it is the single-leafed ash (Fraximus anomola). In protected places where over-grazing by sheep has not exterminated them, there are numerous flowering annuals of brilliant and varied hues. And, of course, there is the usual large number of cactus and yucca characteristic of desert regions. (:gee Fig. 4)

Due to the almost total absence of fossils in the rock formations of the Arches National Monument, the stratigraphy has been determined almost entirely on stratigraphic position and lithology. The oldest rock formation in the area is Triassic Chinle, which is exposed in the bottom of Salt Wash in the east end of the Arches area, where it forms a steep slope from the base of vertical Wingate cliffs to the bottom of the canyon. Above the Wingate which was not measured, but

estimated at 250 to 300 feet, occurs a series of lavender colored, coarse grained sandstones and some thin shale beds that form a stepping platform up to the base of the Navajo Sandstone. This sandstone has been identified as the Kayenta formation because of its lithologic characteristics and position between two easily identified formations. Its thickness was estimated at 225 feet.

The Navajo Sandstone which forms the gently sloping platform on which the arch-building formations rest is a light cream to buff, heavily crosbedded formation whose thickness was determined by alidade observations at 390 feet.

The contact between the Navajo and Carmel formations was chosen where the cream colored sands change definitely to the deep brown-rod color, characteristic of the Carmel sediments. This formation while not measured is 60 to 70 feet thick, and exhibits a crinkly condition that as yet has not been explained. The crinkling has distorted the overlying Entrada Sandstone and makes any definite contact difficult to define.

It is impossible to measure exactly the thickness of the Entrada Sandstone in the area, but a close calculation from alidade observations indicates that there is 380 feet exposed at the Arches and at the Devil's Garden.

The formation is massive, generally buff cross-bedded sandstone, differing, from the Navajo in that it is a darker buff with cross-bedding much less extensive and sweeping in character. Numerous small cavities occur along bedding planes and give a honeycombed effect to the surface of an exposure. (See Fig. 5) The upper 50 or 75 feet of this formation is white, coarser grained, unevenly cemented sandstone.

Resting on the slightly undulating surface of the Entrada Sandstone is the Summerville formation, a thin gritty shale 32 feet thick, composed of alternate layers of red, greenish and white shale and impure sandstone. Measurement of the formation was made with a hand-level some three miles west of Willow Springs in the unsurveyed area of T S, R 21 E. The Summerville occurs as a thin band in the topography below heavy ledges of Salt Wash Sandstone and above long gentle platforms of Entrada Sandstone, or as long snaky ridges on the Entrada which forms the "slick-rock" bench around Willow Springs and southeast and west of Yellow-Cat Knolls.

The Morrison formation composed of sandstone and shales, is exposed in the Yellow-Cat district to the extent of 500 feet. The lower part, essentially layers of heavy cross-bedded, often conglomeritic sandstone with

occasional shale breaks is known as the Salt Wash member of the Morrison. The upper shale beds are variegated gray, green, lavender and pink, eroded into intricately complicated topographic designs. The formations just described of Morrison age contain abundant fossil remains of dinosaur bones. Known bone deposits occur within a hundred feet of the base and range some 300 feet above. Eroded fragments of silicified bone occur widely over the surface and in places are so thickly strewn as to almost completely cover the ground. Embedded bones occur one or two at a place and do not seem to be with a complete skeleton, but there is little doubt that careful search would disclose more or less complete deposits.

The Dakota sandstone and younger formations have not been identified within the boundaries, but occur in close proximity to the north end of the Yellow-Cat section and on the east end of the Devils Garden where the formations dip steeply and fault, throwing. beds of Mancos shale in contact with the Chinle formation.

The warping and folding that accompanied the uplifting of the La Sal Mountains is no doubt the cause of the structural relief that made possible the unique erosional forms to be seen in the area. The Arches are located on the north flank of the Courthouse Syncline,

on the west side of the Colorado River. The rocks dip gently to the westward and to both sides forming an open anticlinal structure rising toward the nearby mountains. At the west end the dips abruptly change , reverse their trend and become a part of the Salt Valley Anticline Structure.

The Devil's Garden owes its grotesque erosion forms directly to the fracturing or vertical jointing of the massive Entrada Sandstone in the course of the formation of the Salt Valley uplift. The jointing parallels the long axis of the anticline and gradually disappears down dip toward the synclinal closure. Running water was not a factor in the formation of the arches and natural bridges found in these two areas as was the case in the White Canyon to the south. Wind erosion, aided by the weather ink; of the rock due to moisture and temperature changes, seems to have been the primary factors in seeking out soft and loosely cemented spots and working them through to large natural arches. In the Devil's Garden a huge hole was bored through a thick massive sandstone slab with the wind, rain and frost as the only apparent tools used in its carving. (See Fig. G)

The large arches, or windows as they are sometimes called, found in the Arches section are not so hard to explain because of their occurrence in the more easily weathered Carmel formation with the massive Entrada Sandstone capping. A freak of natural erosion forms is found in the formation of a double arch, Rising from a common base, two long delicate arms at right angles to each other reach to the nearby cliff. A short distance away two large windows have been carved through the cliffs -- massive and heavy. No less remarkable is the carving of the high rock mesas in which 1;he arches occur. Long fingers of rock, deep gorges and channels with irregularly carved sides.

The Yellow-Cat Knolls composed, as they are, of shale and easily eroded grit are located in a structural depression, and being protected from weathering because of their structural position have persisted and withstood the erosion that is gradually stripping these softer formations from the slick-rock bench.

Though nothing of economic value is being produced from the Arches National Monument or immediate vicinity, a consideration of economic possibilities is important because of the active prospecting in the vicinity for gas and oil. Should a productive oil horizon be found

in the Salt Valley Anticline, a large part or all of the National :Monument would become favorable for oil production because of its close relationship to that structure. The Yellow-Cat district has been actively worked for Vanadium ore which occurs in the Salt Wash Sandstone, but mining operations ceased a few years ago when larger more .easily processed deposits made production here unprofitable. The Paradox formation of Pennsylvanian age, exposed in Salt Valley, is known to contain salt, gypsum, and some potassium salts. The results of core drilling conducted in the valley are not known.