VALLEY OF FIRE STATE PARK
A large area of brightly colored rock of the Aztec Sandstone is exposed at
Valley of Fire State Park, about 45 miles northeast of Las Vegas. The sandstone solidified from a huge area of shifting dunes that existed 200 to 175
million years ago, in Jurassic time, when the region lay within 10 degrees
of the equator. The sea of sand was similar to the Sahara Desert today. The
source of the sand was westward-flowing rivers eroding the enormous
Appalachian Mountains that formed during the assembly of Pangaea. The
Aztec Sandstone, which is also exposed at Red Rock Canyon west of Las
Vegas, is equivalent to the Navajo Sandstone of the Colorado Plateau.
Prior to Cenozoic time, the Aztec Sandstone was much closer to the outcrops of Navajo Sandstone in southwestern Utah; it has since been transported to its current position by extensional Basin and Range faulting.
The Aztec Sandstone is composed of well-rounded grains of almost
pure quartz sand with no clay or silt. A prominent feature of the sandstone exposures is the crossbedding, which forms when the wind shifts
directions. As the dune field got buried by successive layers of sand, the
grains of sand gradually cemented together into hard sandstone. The
color of the sandstone is attributed to minerals, particularly red iron oxide
(hematite) and hydroxide that coated the grains during deposition and to
some extent sulfides, and to the remobilization of minerals as groundwa-ter moved through the rock during and after the sand solidified into rock.
To reach Valley of Fire State Park, take exit 75 from I- 15 north of
Las Vegas. The road crosses an expanse of dry desert for 7 miles before
crossing a slight rise that marks the California Wash fault, an active
and potentially dangerous fault (see road guide I- 15 in this chapter).
After crossing the fault, the road passes into Paleozoic rocks of two dif-
ferent Sevier thrust sheets. The erosion of the overlying thrust sheets
here opened a window into the Jurassic rock below.
From the west entry station to east of the visitors’ center, the road
parallels the Valley of Fire Wash, which has carved the valley along the
axis of an anticline. Exposed in the core of the anticline are the easily
eroded mudstones, siltstones, and sandstones of the Triassic Moenkopi,
Chinle, Moenave, and Kayenta Formations. The more resistant, younger
Jurassic Aztec Sandstone is preserved on both sides of the anticline, as
are the very resistant limestones to the south of the valley. Remnants of
the Horse Spring Formation, deposited on the landscape in Miocene
time, are also visible from the highway.
Most of the points of interest in the park are in the Aztec Sandstone
to the north of the Valley of Fire Road, and some side roads provide
access in that area. The sandstone mass is crisscrossed by joints and
faults, along which erosion has created crevices, passageways, and
drainages and lots of nooks and crannies. Two miles into the park is a
turnoff to the north for Atlatl Rock, known for its petroglyphs, which
were carved into the desert varnish on the sandstone by early peoples
who lived in the area about 3,000 years ago. Another reason to climb
the metal staircase to the petroglyphs lies overhead, in the sandstone
slab overhanging the petroglyphs at the top of the stairs. Look closely
to find approximately eight mammal-like reptile footprints on the bottom of the slab. These fossil tracks are known as Brasilichnium and are
thought to have been made by a small mammal-like reptile. Few body
fossils of the unknown creature have been preserved. Across the road
from the Atlatl Rock turnoff is a turnoff to see petrified logs, remnants
of ancient pines now preserved along the crest of the Valley of Fire
The visitors’ center is situated at the base of the cliffs north of the
road. Inside, along the windows looking south across the valley, is a
discussion of the geologic history of the area. The view south is of the
Muddy Mountains, composed of gray Cambrian through Pennsylvanian strata of the Muddy Mountain thrust sheet.
Making road trips more
interesting for over 40 years!
View southeast from the area of the
west entry station to Valley of Fire
State Park. The orange-red Aztec
Sandstone contrasts vividly with the
gray Paleozoic rocks of the Muddy
Mountain thrust sheet. In the mid-dleground, the Cambrian Bonanza
King rocks are nearly vertical and
are overlain by the reddish-brown
Miocene Rainbow Gardens Member
of the Horse Spring Formation. The
banded gray strata on the far left
horizon are Cambrian carbonates.
Roadside Geology of
416 pages • 6 x 9 • color
$26.00, paper • Item #200