Research: Devils Garden Lava Field

An unnamed lava blister cave that lies in the middle of the Devils Garden lava field. This small
lava cave is one of many volcanic landforms associated with the Derrick Lava Tube System.

Devils Garden Project

INTRODUCTION | GEOLOGY AND VOLCANIC LANDFORMS | PREHISTORY | OBSIDIAN STUDIES | REFERENCES

INTRODUCTION

Click here for an area view of the Devils Garden

Location of the Devils Garden lava field, south-central Oregon.

The Devils Garden is a 45 square mile late Pleistocene to very early Holocene basalt flow and showcase of different varieties of recent volcanic landforms. The lava field is located along the northern periphery of the Fort Rock Basin in the same vicinity as two other recent basalt flows. In coordination with the University of Oregon, we are currently planning archaeological and geochemical studies of archaeological resources in the Devils Garden vicinity as well as an inventory of recent volcanic landforms.

GEOLOGY AND VOLCANIC LANDFORMS

Designated as a Wilderness Study Area (WSA) in the 1980's, the Devils Garden basalt flow is a collection of thin, primarily pahoehoe lava flows that originated from two different vent areas (U.S. Department of the Interior 1985). One of the vents is the marked by "The Blowouts" two unusually large spatter cones and a group of small spatter cones and ramparts. The main vent area, located in the upper northeast quadrant of the lava field, is marked by a low cinder and spatter cone. A prominent lava channel runs to the north and many small lava tubes can be found in the overflow levees of this former lava channel. Fluid basalts from the main vent also flowed to the south through a large tube and fed the lower (southern) part of the lava field. The remnants of this lava tube system can be traced through a series of collapsed and intact lava tube segments, collapsed lava ponds, and pressure plateaus for at least three miles (4.8+ km). Derrick Cave is the largest of the intact lava tube segments although many other smaller caves can be found near the main lava tube system, particularly in the Derrick Cave area. The lava field and lava tubes have been briefly described by several researchers, including Peterson and Groh (1963, 1965), Allison (1979), Larson (1982), Forbes (1973), and Skinner (1983).

Geologic sketch map of the northern portion of the Devils Garden lava field (excerpted from Peterson
and Groh 1965:23). Qyb = Youngest basalt flows of the Devils Garden; Qbu = Older basalts;
Qcc = Basaltic cinder cones; Tab = Vitrophyre and rhyodacite domes of undertain age.

The cinder cone visible at the lower righthand corner of the photograph marks the main Devils Garden vent.
A prominent lava channel runs to the north (up) from the vent. The major channel that fed the flow heads off
to the south and soon leads to Derrick Cave, the largest lava tube found in the area.

High altitude aerial photograph of the Little Garden area of the flow. The "Blowouts", two unusually large spatter
cones, lie near the righthand edge of the photo. The darker elongated areas between the Little Garden and those cones are
collapsed lava ponds that were originally filled by the lava tube tube running beneath them. When the eruption
ceased, the cooled rock crust over the ponds collapsed into the void left by the drained basalt.

The basalt volcanic landforms that are found associated with this lava flow are unusually diverse. Surface landforms include different varieties of pahoehoe lava, cinder cones, spatter cones, spatter ramparts, lava blisters, pressure ridges, pit craters and lava channels. Subsurface landforms and surface expressions linked with the Derrick Lava Tube system consist of many different lava tube caves, collapse depressions, pressure plateaus, hornitos, tumuli, and inflated and collapsed lava ponds.

Left: Derrick Cave, the largest uncollapsed segment of the Derrick Lava Tube System.
Right: The Blowouts, two exceptionally large spatter cones found at the eastern margin of the flow.

The age of the Devils Garden lavas is not well known, although some geomorphic evidence suggests an early Holocene date for the eruption. Shells collected from a former Pluvial Fort Rock beach terrace located at an elevation of 4,386 feet yielded a radiocardon date of about 13,000 years. (Bedwell 1973). Uneroded basalts from the Devils Garden lava field reach an elevation in this same area of 4,374 feet, evidence that the maximum age of the flow is no more than about 13,000 years. The entire flow is also blanketed by 6,845 year-old (radiocarbon years) tephra from Mount Mazama, conveniently providing a minimum age as the date of that eruption.

View of the Little Garden in the middle distance. This island of older rhyolitic rock (including a
minor obsidian source) projects from the Devils Garden lava field. Taken facing east from a
pressure plateau that rises above the Derrick Lava Tube System.

PREHISTORY

Little is currently known of the prehistoric significance of the Devils Garden area. The southern edge of the lava field borders Cougar Mountain - a major source of obsidian located along the northern margin of the Fort Rock Basin. It is likely that the unique lava flow environment of the Devils Garden played a role in the long history of occupation in the basin, either as a seasonally-utilized resource area or as a travel corridor to nearby Newberry Caldera. Or both. The rugged and sometimes timbered basalts of the flow could provide a productive habitat for game - caves and other volcanic landforms might provide environments for late-season persistent snow or perennial ice and water. In addition, at least two minor sources of obsidian are found associated with the upper part of the flow.

Two examples of the prehistoric stone circles that are sometimes found on the smooth pahoehoe surfaces of the basalt flow.

Above: The entrance to a small perennial ice cave associated with the Derrick Lava Tube System. These year-round
sources of water were often significant prehistoric resources in the arid Great Basin environment.

Below: Bamboo walking stick rests on the ice surface in the cave pictured above.

OBSIDIAN STUDIES

Preliminary X-ray fluorescence analysis studies have been completed for a collection of obsidian debitage collected at a severely disturbed site in the northern part of the flow (see below). Although we had predicted that nearby Cougar Mountain would prove to be the source of most of the artifacts, only 11 of the 74 analyzed flakes were found to originate from that source. The trace element composition of the remaining 63 flakes indicated that most came from Quartz Mountain, another major regional prehistoric source of obsidian located about 10 mi (16 km) to the north of the site. Three additional artifacts were represented by single artifacts. Two of these are local sources found within (Little Garden) or very near (Squaw Ridge) to the Devils Garden lava field. The near absence of obsidian from the Newberry Caldera sources situated about 25 mi (40 km) to the northwest suggests that the Devils Garden was primarily integrated into a procurement range that did not directly or significantly include Newberry Caldera. This conclusion is also supported by the near absence of Fort Rock Basin obsidian sources at Newberry Crater sites (Hughes 1999) combined with a similar paucity of artifacts from Newberry Caldera source at Fort Rock Basin archaeological sites (Jenkins et al. 1999; Skinner et al. 2004). Interestingly, obsidian from the Quartz Mountain source is commonly found at sites in both Newberry Caldera and the Fort Rock Basin.

Scatterplot of strontium (Sr) plotted versus zirconium (Zr) for artifacts collected at a site near the Little Garden.

Obsidian Source	N =	Percentage
Cougar Mountain	11	14.8
Little Garden	1	1.4
Newberry Volcano	1	1.4
Quartz Mountain	60	81.0
Squaw Ridge	1	1.4
Total	74	100.0

Summary of results of trace element analysis of obsidian artifacts.

REFERENCES

Allison, Ira S. 1979. Pluvial Fort Rock Lake, Lake County, Oregon. Bedwell, Stephen F. 1973. Fort Rock Basin: Prehistory and Environment. University of Oregon Books, Eugene, Oregon.

Benedict, Ellen M. and Ben A. Benedict. 1982. Roadlog to Caves and Other Volcanic Landforms of Central Oregon. In Caves and Other Volcanic Landforms of Central Oregon, edited by L. Sims and E. Benedict, pp.12-38. National Speleological Society, Huntsville, Alabama.

Forbes, Charles F. 1973. Pleistocene Shoreline Morphology of the Fort Rock Basin, Oregon. Unpublished Ph.D. Dissertation, University of Oregon, Eugene, Oregon.

Hughes, Richard E. 1999. Appendix B: Trace Element Concentrations of Obsidian Artifacts. In Newberry Crater: A Ten-Thousand-Year Record of Human Occupation and Environmental Change in the Basin-Plateau Borderlands, by Thomas J. Connolly, pp. 259-271. University of Utah Anthropological Papers No. 121, Salt lake City, Utah.

Jenkins, Dennis L., Craig E. Skinner, Jennifer J. Thatcher, and Keenan Hoar. 1999. Obsidian Characterization and Hydration Results of the Fort Rock Basin Prehistory Project. Paper Presented at the 52nd Northwest Anthropological Conference, Newport, Oregon, April 1999.

Larson, Charles V. 1982. Descriptions of Central Oregon Caves: With Special Emphasis on Ice Caves. In An Introduction to Caves of the Bend Area, edited by C. V. Larson, pp. 9-74. National Speleological Society, Huntsville, Alabama.

Peterson, Norman V. and E. A. Groh. 1963. Recent Volcanic Landforms in Central Oregon. Ore Bin 25:33-45.

Peterson, Norman V. and E. A. Groh. 1965. Lunar Geological Field Conference Guidebook. Department of Geology and Mineral Industries Bulletin 57, Portland, Oregon.

Skinner, Craig E. 1983. The Derrick Lava Tube System: Oregon's Third Longest? Speleograph 19(1):3-5.

Skinner, Craig E., Jennifer J. Thatcher, Dennis L. Jenkins, and Albert C. Oetting. 2004. X-Rays, Artifacts, and Procurement Ranges: A Mid-Project Snapshop of Prehistoric Obsidian Procurements Patterns in the Fort Rock Basin of Oregon. In Early and Middle Holocene Archaeology of the Northern Great Basin, edited by Dennis L. Jenkins, Thomas J. Connolly, and C. Melvin Aikens, pp. 221-232. University of Oregon Anthropological Papers 62, Eugene, Oregon.

U. S. Department of the Interior. 1985. Draft Oregon Wilderness Environmental Impact Statement: Volume II. U. S. Department of the Interior.

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Last Updated: 03/28/2007
Northwest Research Obsidian Studies Laboratory