Turning left (northwest) at the intersection with the paved park road,
we enter Devils Garden—another large maze of towering red fins separated
by narrow slots, which resembles the Fiery Furnace. After a third of a
mile, we reach stop 24 and walk 100 feet or more to the north for a good
view of Skyline Arch (fig. 48). This arch is very appropriately named,
as it forms the skyline viewed either from the road on the south or from
the campground on the north, from points south of the amphitheater. Less
well known is the fact that Skyline Arch is clearly visible to the naked
eye or through binoculars from stretches of Highway I-70 (or old U.S.
Highways 6 and 50) about 11 miles to the north. Most arches and other
erosion forms do not change appearance much from day to day or year to
year, but some, like “Baby Arch” (fig. 15), show evidence of relatively
recent origin. In November 1940 (Abbey, 1971, p. 42) Skyline Arch
suddenly doubled in size by the fall of a large rock that occupied what
is now the northwest half of the arch. Photographs taken before and
after this event appear on pages 24 and 25 of the road guide and also in
the museum at the Visitor Center.
[Illustration: TOWER ARCH, on Klondike Bluffs, viewed eastward. Arch
is in Slick Rock Member but tower on left, after which arch was
named, is capped by a protective layer of the resistant Moab Member.
Opening is 88 feet wide and 43 feet high. Photograph by Robert D.
Miller. (Fig. 47)]
[Illustration: SKYLINE ARCH, viewed north from point about 100 feet
north of stop 24, in Slick Rock Member. Although fins are vertical,
note that the strata seem to dip about 15° to the right, although
the actual dip is to the northeast. (See fig. 50.) (Fig. 48)]
Another half mile brings us to a one-way (to right) loop at the end of
the park road. Just beyond the beginning of the loop is a parking lot
and very attractive picnic area containing several picnic tables shaded
by piñon pines at the foot of a towering red fin of the Slick Rock
Member. Just north of this picnic ground, a paved side road leads
eastward into a truly beautiful, well-equipped campground comprising
both back-in and drive-through campsites for trailers, campers, or
tents; three pairs of modern restrooms, hydrants, and drinking
fountains; and an amphitheater, where illustrated campfire talks are
given nightly during the summer. The east end of the campground is shown
in figure 49.
[Illustration: CAMPGROUND IN DEVILS GARDEN, viewed northwestward
across turn-around at southeastern end. (Fig. 49)]
Devils Garden in general and the campground in particular are on the
crest of a ridge separating Salt Valley to the southwest from the Sagers
Wash syncline to the northeast, which lies north of Yellow Cat Flat and
north of the area shown in figure 1. From the higher parts of the
campground striking views are to be had toward the north and northeast,
particularly late in the afternoon, as shown in figure 50.
[Illustration: VIEW NORTH FROM CAMPGROUND, in late afternoon.
Reddish Slick Rock Member capped by light-colored Moab Member are
seen dipping northeastward toward Sagers Wash syncline. Book Cliffs,
north of Thompson, are 16 miles north on left skyline. (Fig. 50)]
In about the middle of the one-way loop at the end of the park road is a
well that supplies water to the campground from early in the spring
until the return of freezing weather late in the fall. The well, which
was drilled in 1962 to a depth of 900 feet, obtains a small amount of
water from the Wingate Sandstone. No water was found in the overlying
Navajo and Entrada Sandstones because of the pronounced dip of the rocks
toward the northeast, which allows any water in these rocks to drain
northeastward (Ted Arnow, written commun., 1963). Water from this well
is pumped to a steel tank in a high part of the campground, whence it
flows by gravity to the three sets of restrooms.
[Illustration: SOUTHEASTERN PART OF DEVILS GARDEN TRAIL, viewed
northwestward. Narrow slot between fins of Slick Rock Member
indicates local spacing of joints. (Fig. 51)]
At the northwest end of the one-way loop is a large parking area for use
by people hiking the Devils Garden trail. This trail leads to seven of
the most interesting arches in the park, all of which are in the Slick
Rock Member, and there are many more farther to the northwest. The
approximate distances to the seven arches are given in the paragraphs
that follow. The trail is paved for about 1 mile as far as Landscape
Arch (fig. 53), but from there to Double O Arch (fig. 56) the trail is
primitive, and the Park Service recommends rubber soles as part of the
trail is on bare sandstone. For these reasons, many visitors hike only
as far as Landscape Arch.
[Illustration: PINE TREE ARCH, viewed northeastward. Opening is 46
feet wide and 48 feet high. Fin is 30 feet thick. (Fig. 52)]
Much of the trail, particularly the first part, lies in a narrow slot
between fins of the Slick Rock Member, as shown in figure 51. After
about half a mile, a side trail to the north leads to a Y, the
right-hand fork of which goes to Tunnel Arch (fig. 14). The left-hand
fork leads to Pine Tree Arch, obviously named for the piñon pine framed
by this arch (fig. 52).
At the end of the improved part of the trail, we reach Landscape Arch
(fig. 53), claimed by the Park Service to be the longest known natural
arch in the world. According to Ouellette (1958) it is 291 feet long and
118 feet high, but Professor Stevens’ measurements indicate it to be 287
feet long and 106 feet high. At its thinnest point on the right, the
span is only 11 feet wide and 11 feet thick. In 1958 three young men
made what was claimed to be the second known ascent of Landscape Arch,
using ropes and other climbing gear, after which they walked across
(Ouellette, 1958). This crossing was made with the permission of a park
ranger, but such permission is no longer given, for the safety of both
the arch and of would-be climbers.
Wall Arch is about a quarter of a mile beyond the end of the improved
part of the trail, and another three-fourths mile brings us to Navajo
Arch (fig. 54) and Partition Arch (fig. 55). A distant view of Partition
Arch may be had just before reaching Landscape Arch. Part of the
remaining trail to Double O Arch (fig. 56) is on the top of a low
sandstone fin, in part between somewhat higher fins and in part above
lower slots.
[Illustration: LANDSCAPE ARCH, viewed southwestward from near end of
improved part of Devils Garden trail. Note that ground beneath arch
is covered by slope wash and near the middle with what appears to be
a small landslide. Slick Rock Member here is more nearly buff than
salmon colored, because of a smaller content of iron oxide. Fresh
breaks and angular blocks of stone at right abutment indicate
relatively recent rock falls. See text for size. (Fig. 53)]
[Illustration: NAVAJO ARCH, viewed northeastward from a branch of
Devils Garden trail. One of few arches having a flat soil-covered
floor. Opening is 40½ feet wide. Photograph by National Park
Service. (Fig. 54)]
Beautiful Double O Arch (fig. 56) is at the end of the Devils Garden
trail about 2½ miles northwest of the trailhead. About half a mile
northwest of the trail’s end is a prominent landmark called Dark Angel
(fig. 57), which is visible in figure 12 and from the unimproved road in
Salt Valley.
[Illustration: PARTITION ARCH, viewed southwestward from near Devils
Garden trail. Arch frames part of south wall of Salt Valley and, on
skyline, mesas south of Moab Valley. Opening is 27½ feet wide and 26
feet high. A smaller opening to the right measures 8½ feet wide and
8 feet high. Photograph by Dawn E. Reed. (Fig. 55)]
[Illustration: DOUBLE O ARCH, viewed about north from northwest end
of Devils Garden trail. Large opening is 71 feet wide and 45 feet
high; small one at lower left is 21 feet wide and 11 feet high. Span
of large opening is 11 feet wide and 6 feet thick. Arch frames a
part of the Book Cliffs about 14 miles to the north. Photograph by
Hildegard Hamilton, Flagstaff, Ariz. (Fig. 56)]
[Illustration: DARK ANGEL, a shaft of the Slick Rock Member that is
an erosional remnant of a once high, narrow fin. About one-half mile
northwest of Double O Arch. Photograph by National Park Service.
(Fig. 57)]
[Illustration: “INDIAN-HEAD ARCH,” in upper Devils Garden. Arch and
most of head are in Slick Rock Member, top of head is basal part of
Moab Member. Opening is 4 feet wide and 4½ feet high. Photograph by
Professor Dale J. Stevens, Brigham Young University. (Fig. 58)]
[Illustration: GEOLOGIC TIME SPIRAL, showing the sequence, names,
and ages of the geologic eras, periods, and epochs, and the
evolution of plant and animal life on land and in the sea. The
primitive animals that evolved in the sea during the vast
Precambrian Era left few traces in the rocks because they had not
developed hard parts, such as shells, but hard shell or skeletal
parts became abundant during and after the Paleozoic Era. (Fig. 59)]
GEOLOGIC TIME
The Age of the Earth
The Earth is very old—4.5 billion years or more according to recent
estimates. Most of the evidence for an ancient Earth is contained in
the rocks that form the Earth’s crust. The rock layers
themselves—like pages in a long and complicated history—record the
surface-shaping events of the past, and buried within them are
traces of life—the plants and animals that evolved from organic
structures that existed perhaps 3 billion years ago.
Also contained in rocks once molten are radioactive elements whose
isotopes provide Earth scientists with an atomic clock. Within these
rocks, “parent” isotopes decay at a predictable rate to form
“daughter” isotopes. By determining the relative amounts of parent
and daughter isotopes, the age of these rocks can be calculated.
Thus, the results of studies of rock layers (stratigraphy), and of
fossils (paleontology), coupled with the ages of certain rocks as
measured by atomic clocks (geochronology), attest to a very old
Earth!
Professor Stevens found 14 arches in what he called upper Devils Garden,
northwest of Double O Arch, and two arches in the northwesternmost
extension of the park known as Eagle Park (fig. 1). One of the unnamed
arches in upper Devils Garden is shown in figure 58. I am tentatively
calling it “Indian-Head Arch,” because of the rather obvious
resemblance.
This ends our journey through Arches National Park, but there remains
for consideration a summary of the principal geologic events leading to
the formation of this beautiful part of the Colorado Plateau and a brief
comparison with the geology of other national parks and monuments on the
Plateau.