[Wildflowers Along the Alder Springs Trail #855, Crooked River National Grasslands, Crook County, OR.]
History
Native Americans lived in this area for several thousand years. Recently cattle grazing took place. The Vogt family had the allotment until 1982 and cattle were removed in 1984. There has been only occasional sheep trespass in the area since then. The area is part of the Crooked River National Grasslands and is administered by the Ochoco National Forest. The land surrounding the trailhead is private but there exists a long-standing public easement.
Geology
The colorful, banded walls of the canyons of the Middle Deschutes River record a spectacular and violent era in the geologic history of Central Oregon. These strata comprise the Deschutes Formation and represent over 3 million years of volcanism along a volcanic front over 60 miles long. These layers represent dozens of volcanic centers and magma batches. The formation is over 2300 feet thick in some places. This formation provides the best exposed and most diverse record of Early High Cascade volcanism yet studied. The layered deposits at Steelhead Falls, Alder Springs, and the Cove are part of the Deschutes Formation.
The Building of the Early High Cascades and the Deposition of the Deschutes Formation
One thinks of current High Cascade volcanoes as being ancient. Actually, they are very young geologically: less than half a million years old. The Deschutes Formation records the development of the ancestors of these modern volcanoes. About 7.6 million years ago (mya), eruptions began from a linear group of volcanoes in the region of the present High Cascades. These eruptions included large and violent flows of glowing ash called ignimbrites (welded and non-welded ash-flow tuffs) which travelled over 25 miles at 50 to 100 miles per hour and were deposited in layers each over 30 feet thick. All living things in the path of these eruptions were destroyed. Over 100 ignimbrites were erupted. They helped to fill the ancestral Deschutes River Basin. Over 225 separate volcanic units have been delineated in the Deschutes Formation. Of these, 75 are ignimbrites, 12 of which are welded, and 24 units have been informally named by geologists.
From 7.6 to 4.4 million years ago, dozens of ash flows, mudflows, airfalls, and other cataclysms occurred as the Early High Cascades were being built. These processes are captured in walls of the Middle Deschutes Canyons. During this time the Deschutes Formation recorded reversals of the earth’s magnetic field and at least 4 former channels for the Deschutes River came and went. Good examples of inverted topography are found in the drainages to the east of Green Ridge. These represent ancient low areas and valleys which were filled by lava and subsequently the surrounding softer sediments were eroded. The ancestral Deschutes River was dammed many times by lava flows and some ash was carried eastward by prevailing winds and fell into lakes. These quiet environments preserved plants and animals as fossils. This type of volcanic activity went on for over 3 million years.
The Development of the High Cascades Graben
There is strong evidence that the Early High Cascades were undergoing east-west extension at the time of the eruption of the Deschutes Formation. As part of this extension, and for reasons that are not well-understood, the central portion of the Early High Cascades Range began to subside about 4.4 mya into a large trench over 3,000 feet deep called the High Cascades Graben (German for “grave”). Green Ridge is the eastern wall of this trench (see diagram). The High Cascades Graben could have been a reflection of the invasion of Basin and Range extension into the Cascades. Fault systems from the Basin and Range Province to the southeast seem to connect to the Green Ridge system. Basalts in the Deschutes Basin and in the Basin and Range are similar. Gravity data suggest older (8 to 13 mya) eras of graben development in the Cascades and the possibility of “nested grabens.” Another theory suggests that the Graben could be related to the oblique subduction of the Juan de Fuca plate under North America and the subsequent generation of tension within the Cascades crust.
After subsidence, the Early High Cascades volcanoes continued to erupt, but ash was not able to get out of the trench and into the Deschutes Basin to the east as it once had. The Deschutes Formation/Early High Cascade volcanoes are not exposed at the surface now because they have been buried by the modern Late High Cascades platform of lavas which is so prominent today. Subsidence of the Graben and movement along the Green Ridge Fault ended about 2.2 mya. Studies also suggest an extensive volcanic highland called the Tumalo Highlands which had a similar style of volcanism and extended east from the Cascades toward Bend during the past 700,000 years.
The Development of the Modern Deschutes River
After the development of the High Cascades Graben, ash could no longer reach the lands to the east. This allowed erosion to become the dominant process in the ancestral Deschutes Basin. The river then proceeded to erode its present canyon over the last 2.2 million years. The Metolius River has been shown to erode its bed at the rate of 200 feet per million years. The layered canyon walls at Alder Springs, The Cove, and Steelhead Falls have a colorful record of this remarkable period of Central Oregon volcanism.
Vegetation
Vegetation in the area is primarily meadow-shrub steppe and juniper woodland.
Meadow-sage Steppe
When visitors to the high desert view the wide-open sage vistas they are actually admiring vegetation of the meadow-sage steppe. The high desert of central Oregon really doesn’t fit the strict botanical or geographical definition of a desert. The Russian word “steppe” is the appropriate botanical term. In pre-Euro-American settlement times, fires would range through this ecosystem on the average of every 20 to 40 years. There were fewer juniper trees and less sage. There were more native bunchgrasses. It was this fabulous forage resource that the early ranchers exploited. Many thousands of head of horses, sheep, and cattle were introduced onto the range in Central Oregon in the 1860’s and 70’s. By the turn of the century, much of Central Oregon had already experienced heavy grazing. One of the threats to native grasslands in our area is the invasion of exotic plants. Cheatgrass, a Eurasian immigrant at the turn of the century, has replaced many of our native annual grasses. Knapweed is increasing as an invader. It too is Eurasian and has been very invasive in Montana and Idaho.
Management Issues
The most significant threat is the invasion of noxious weeds. In 1996 the NPSO in cooperation with the Grasslands began a program to eradicate the teasel, knapweed, sweet clover and mullein that came in with cattle grazing. Grazing is no longer permitted in this area which is a candidate for Wild and Scenic River Status. The sweet clover has been eradicated and the teasel is much reduced.