The Flagstaff Analytical Laboratory
Rocky Mountain Research Station-Flagstaff, USDA-Forest Service
Southwest Forest Science Complex
2500 S. Pine Knoll Drive
Flagstaff, AZ 86001
Phone: (928) 556-2044

Historic accounts of the stream channel prior to water diversion suggest an extensive travertine system.  In the late 1800's, the naturalist Charles Lummis (1891) reported that Fossil Springs water was so impregnated with mineral that  "...it was constantly building great round basins for itself, and for a long distance flows over bowl after bowl".  But, a later visitor,  F.W. Chamberlain (1904) noted that  "...the travertine structures persisted in a two mile reach of the creek.  The largest pool seen was behind a ten foot tall travertine dam, 50 to 60 yards long, 20 to 30 feet wide, and approximately 20 feet or more deep".

In 1994, the Federal Energy Regulatory Commission (FERC) in cooperation with the U.S. Forest Service began a review of Arizona Public Service Company's (APS) license to divert flow from Fossil Creek for power generation.  The Federal Power Act requires water power operators to be periodically reevaluated so that, if warranted, the operation may be either discontinued or modified, to reflect changing social values, operational advancements, or other factors (FPA, 1920). A final decision by FERC is still forthcoming.

Fossil Springs is located just below the edge of the Mogollon Rim, at the southern margin of the Colorado Plateau, in Fossil Creek Canyon.  North of Fossil Springs the area is characterized by steep-walled canyons cut into flat-lying Paleozoic sedimentary rocks, while south of the springs the canyon is composed of Tertiary volcanic rocks.  Approximately 1,000 m of Paleozoic and Cenozoic strata are exposed within the canyon. Paleozoic stratigraphy include the Mississippian Redwall Limestone, Pennsylvanian Naco Formation, Pennsylvanian/Permian Supai Formation, Permian Schnebly Hill Formation, Coconino Sandstone and Permian Kaibab Formation  (Blakey, 1990).  In the northeastern portion of the canyon the Paleozoic strata are covered by Tertiary volcanics ranging in thickness from 10 to 100 m. South of Fossil Springs, the volcanic rocks, chiefly dark-gray basalt and yellowish-gray tuff, thicken abruptly to more than 600 m along an ancestral Mogollon Rim (Twenter, 1962), where they were deposited in an ancestral lowlands.  A basalt flow located approximately 400 m above the floor of the Fossil Creek Canyon produced a potassium-argon age of 10.16 + 0.22 m.y (Peirce et al., 1979), giving a minimum age of formation of the ancestral Mogollon Rim.

A unique feature of the area is a prehistoric travertine deposit (Pleistocene and Holocene) that forms a conspicuous bench above Fossil Springs (Weir and Beard, in press). Remnant travertine formations begin approximately
0.5 km below the springs and persist for approximately 7.5 km downstream.  Due to diversion of spring water for power generation, modern travertine deposits in the natural channel only form where baseflow is returned to the natural channel.  Presently, baseflow in the natural channel and subsequent downstream travertine deposition occur as a result of the Irving diversion dam leaking  and at the Irving Plant tailrace, which discharges a small proportion during normal operations (Federal Energy Regulatory Commission, 1997).  Areas of large travertine deposits similar to the historic Fossil Creek deposits are widely recognized as unique natural wonders.

An unusual combination of natural processes must take place to form travertine.  The process begins when water becomes elevated in dissolved CO₂(g) through interactions with the soil zone, carbonate aquifers, organic material, or regional geothermal activity. Upon emerging, the carbon dioxide outgasses as the water begins to equilibrate with atmospheric conditions. This outgassing results in an increase of calcite (CaCO₃) in the water above saturation.  Increased calcite concentration eventually surpasses a critical level of supersaturation and CaCO₃ begins to precipitate as travertine.

Precipitatescan occur on both organic or inorganic substrates.  Obviously, stream ecology largely affects the relative amounts of deposition on organic versus inorganic substrates.  Simply stated, the more organic surface area available, the more likely deposition will occur on organic substrates. Purely inorganic deposits typically form in cavernous areas and result in stalactites, flowstone, cave popcorn, and cave pearls.  Organic deposits occur on living aquatic organisms such as algae, mosses, diatoms, and any other organic detritus (leaves, sticks, etc.) that may be within the fluvial system.  Crystal morphology for both the inorganically associated and the organic travertine deposits are composed of a wide range of calcite morphologies and sizes.

Fossil Creek was the study site for a project quantifying travertine deposition from carbonate rich water. Fossil Creek is fed year round with water emanating from Fossil Springs.  These waters are usually diverted by a dam located just below the springs, through a flume, to a hydroelectric  power plant 6.7 km downstream. However, during the spring of 1996 water was sampled during full base flows in the natural channel during generator maintenance. Sampling was later repeated in this same section during the normal seepage flow from the diversion dam.


This study was designed to observe the downstream geochemical evolution of the spring water for all the major chemical constituents during full base flows as well as during lower seepage flows. In the 6.7 km stretch below Fossil Springs, analyses indicate ~12 metric tons per day of calcium carbonate is precipitated from full base flows (Malusa 1997; Malusa et al., in review). Currently travertine dams occurs only below the Irving hydroelectric power plant due to the return of a small proportion of total flow to the natural channel.

This research demonstrates that geochemical processes exist to restore the degraded travertine system in Fossil Creek. Historical accounts and geochemical analyses indicate the majority of travertine deposition would occur along a 4mile reach beginning at Fossil Springs. Travertine formations would occur at a rate proportional to the amount of spring discharge allowed to flow down the natural channel. A sequence of long  periods building travertine dams followed by occasional flood events that destroy some or all of the travertine dams produces an active morphology in the Fossil Creek channel. Restoration of travertine dynamics from resumption of natural flows would create a rare natural phenomenon and an opportunity to further study processes of travertine formation.