Devils Postpile
                     NATIONAL MONUMENT • CALIFORNIA


DEVILS POSTPILE NATIONAL MONUMENT

Along the picturesque Middle Fork of the San Joaquin River at 2,300
meters (7,600 feet) on the western slopes of the Sierra Nevada lies
Devils Postpile National Monument. The 324-hectare (800-acre) monument
near the resort community of Mammoth Lakes includes one dominant
feature: a formation of columnar basalt known as Devils Postpile.
Another important feature in the area is Rainbow Falls. Pumice is the
dominant rock-type encountered, but basalt, andesite, rhyodacite, and
granite lie just under the surface and crop out in many places. Plants
and animals are typical of lodgepole pine and red fir forests. To see
the features of the monument one must walk.


DEVILS POSTPILE

The formation of Devils Postpile began when basalt lava erupted in the
valley of the Middle Fork of the San Joaquin River. As lava flowed from
the vent, it filled the valley near the Postpile to a depth of 122
meters (400 feet). Recent radiometric dating of rocks thought to
correlate with basalt of Devils Postpile suggest an age of less than
100,000 years.

Surface cracks formed when tensions caused by the shrinkage of the
cooling lava were greater than the strength of the lava itself. Each
crack branched when obtaining a critical length and together with other
cracks formed a pattern on the surfaces of the flow. Ideal conditions
allowed surface cracks to deepen, resulting in the formation of long
columns.

    [Illustration: uncaptioned]

Approximately 10,000 years ago, glaciers flowed down the Middle Fork of
the San Joaquin River. This moving ice easily overrode the fractured
mass of lava and quarried away one side of the Postpile, exposing a
sheer wall of columns 18 meters (60 feet) high. Many fallen columns now
lie fragmented on the talus slope below.

A hike to the top of the Postpile reveals not only a cross section of
the posts, but the most interesting effect of the ice—polished tops of
the basalt columns. Here, the column ends are exposed like a tiled floor
and exhibit parallel striations where the glacier dragged rocks across
them.

Even though Devils Postpile is among the world’s finest examples of
columnar-jointed basalt, it is not unique. Giant’s Causeway in Ireland
and Fingal’s Cave in Scotland are similar formations.


SODA SPRINGS

Nearby mineral springs are evidence of recent local volcanic activity.
The Soda Springs lie on a gravel bar in the San Joaquin River just north
of the Postpile. Here, gases driven upward from hot areas deep in the
earth combine with ground water to produce cold and highly carbonated
mineralized springs. The iron present in Soda Springs water oxidizes on
exposure to the atmosphere and stains river gravel a reddish brown.

    [Illustration: uncaptioned]


SAFETY

For your safety, remember that there are hazards in the mountains that
usually do not exist in the city. Stay on designated trails; these are
the safest places to hike. Use caution when viewing features from near
cliff or gorge edges. Footing can be hazardous. WARNING: Bears inhabit
the monument. Proper food storage is required by Federal law.

    [Illustration: uncaptioned]

  MONUMENT BOUNDARY
  CAMPGROUND
  TO U.S. 396 & MAMMOTH LAKES
  RANGER STATION (_El. 7,560 ft._)
  SOTCHER LAKE
  _Soda Springs_
  DEVILS POSTPILE
  _King Creek Trail_
  _San Joaquin River_
  REDS MEADOW
  THE BUTTRESSES
  _Middle Fork_
  _John Muir Trail_
  _Boundary Creek_
  RAINBOW FALLS (101 feet)
  LOWER FALLS

    [Illustration: uncaptioned]


RAINBOW FALLS

At Rainbow Falls the Middle Fork of the San Joaquin River drops 31
meters (101 feet) over an andesite and rhyodacite cliff. It is thought
that after the last glacier melted, the river flowed downstream from
Devils Postpile in channels about 457 meters (1,500 feet) west of its
present course. Flowing in these older channels, it cut through the
rhyodacite lava down to granite, leaving a cliff of rhyodacite for its
eastern bank. Then, some distance upstream, the waters were diverted
eastward. The river left its bed to follow its present path until it
returned to the old channel, by cascading down the cliff it had earlier
cut. Thus Rainbow Falls was formed. A stairway and short trail lead to
the bottom of the falls, where numerous flowers and grasses form an
enchanting garden. Cars may be driven to within 1.6 kilometers (1 mile)
of the falls via the road to Reds Meadow.


ABOUT YOUR VISIT

The monument is reached by a 16-kilometer (10-mile) drive west from U.S.
395 on S.R. 203 to Minaret Summit, then by 11.2 kilometers (7 miles) of
paved narrow mountain road. The monument is administered by the National
Park Service, U.S. Department of the Interior. For more information
write: Superintendent, Sequoia and Kings Canyon National Parks, Three
Rivers, CA 93271. Park rangers are on duty to assist you, to conduct
interpretive activities, and to enforce the regulations. _Closed in
winter._

_Accommodations and services._ Meals, lodging, groceries, gasoline,
horses, and other facilities and services are available at Mammoth Lakes
or nearby Reds Meadow.

_Camping._ A campground is maintained near the ranger station from about
July 1 to October 15, depending on the weather.

_Hiking._ Trips may be made north or south on the John Muir Trail and
west on the King Creek Trail. The monument also has several short
trails.

_Fishing and hunting._ Fishing is permitted in the monument, but hunting
is prohibited. A California angling license with appropriate stamps is
required for persons 16 years of age or over.

_Pets._ Pets are permitted in the monument only if they are kept under
direct physical control at all times.


                         National Park Service
                    U.S. DEPARTMENT OF THE INTERIOR

  GPO 1984—421-613/317 Reprint 1984




                          Transcriber’s Notes


—Silently corrected a few typos.

—Retained publication information from the printed edition: this eBook
  is public-domain in the country of publication.

—In the text versions only, text in italics is delimited by
  _underscores_.