Geology of the Teanaway Community Forest
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GEOLOGY OF THE TEANAWAY COMMUNITY FOREST Holocene Glaciers from the high mountains to the west advanced down the Cle Elum and Yakima river 11.7 ka Teana ge valleys. The glaciers blocked the Teanaway wa y Rid Cle Elum River and created a temporary lake. When the Ri Pleistocene dge TEANAWAY glaciers melted and retreated up the valley, the ice-dammed lake lake drained and left behind weak layers of silt QUATERNARY glacier COMMUNITY FOREST 1.8 Ma and clay. Pliocene 5.3 Ma glacial sedimentbedrock Miocene NEOGENE CENOZOIC 23.0 Ma Oligocene Between 17 million and 6 million years ago, 33.9 Ma several fissures near the Washington–Oregon Eocene border erupted molten basalt, burying an area 56.0 Ma larger than the state of New York. Paleocene PALEOGENE 66.0 Ma These rocks are called ‘flood basalts’ and form the flat land in eastern Washington. The MESOZOIC AND OLDER flood basalts covered everything in their path, Grande Ronde flood basalt filling up river beds like the Yakima River near Ma; millions of years ago (covered 58,000 mi2) Cle Elum. ka; thousands of years ago INTERESTING FACTS ● Teanaway Basalt is the source of the “Ellensburg Blue” agate. ● Glaciers once filled the Yakima and Cle Elum river valleys. These Warm groundwater rich in silica flowed through the basalt glaciers blocked the Teanaway River and formed a temporary and formed the agate. The agate erodes from the basalt and lake. is transported toward Ellensburg by rivers. ● The Eocene was a period of tectonic tumult in Washington. The ● Rocks here are from the Eocene epoch and record a time before Earth split and formed narrow basins and sinuous mountains. the Cascade Range existed. Instead, you would have found Teanaway Basalt poured out from thousands of fissures and meandering rivers, low hills, and swamps instead of mountains. filled the valleys. Because the basalt is so resistant to erosion, The river deposits and swamps were compressed by overlying these ancient valley bottoms are now high ridges. rock and heated by the Earth to become sandstone and coal. ● The climate was significantly warmer during the Eocene, ● Coal was mined here for about 80 years—the product of and large palm-like trees are occasionally found as fossils in ancient swamps buried and heated over time. These swamps rocks of this age. Horses—originally the size of modern-day are preserved in rocks along Cle Elum Ridge. coyotes—first appear in the fossil record at this time. FOR MORE INFORMATION BELLINGHAM 5 395 97 Find more geology info at: www.dnr.wa.gov/geology 2 SPOKANE SEATTLE 2 101 90 Find trail maps, recreation activities, campgrounds, and information about how to support 90 Exclamation Point Rock (above) is made from a 12 OLYMPIA 195 the Teanaway Community Forest at: 395 PULLMAN resistant sandstone layer of the Roslyn Formation. 12 YAKIMA 12 97 It is point of interest “A” on the geologic map. www.dnr.wa.gov/Teanaway 5 VANCOUVER GEOLOGY OF THE TEANAWAY COMMUNITY FOREST POINTS OF INTEREST Geologic Map 0 2 4 mi M i d d l Sasse e ● Exclamation Point Rock is Eocene sandstone from the Roslyn Mt. F Formation. It formed when surrounding weaker rocks eroded o r k away. Community Forest Teanaway T e a ● Extensive logging over the past century has caused bedrock n a Teanaway w C a Butte channels to replace gravel beds. Gravel beds are better W y e Yellow s (outer boudary) habitat for spawning fish. Efforts to restore the river are t 29 Hill R T F i e v Pines underway to improve habitat. o e a r r k r n e a T v ea i ● Landslides (light yellow areas on the map) are relatively n R w a y w B a a common in Washington due to steep slopes and heavy pre- a y y w a n cipitation. Physically weak layers, such as clay or silt in glacial R a i v e e Indian T Red Top lake sediments, makes landslides more likely. Steep slopes or r k Mt. r Camp o Mineral layers that dip steeply can also have more landslides. F Springs t h r o N The Grand Ronde Basalt formed when molten basalt erupted ● from fissures near the border of Washington and Oregon. The B R i 97 d basalt filled the lowlands of eastern Washington and flowed g up the ancient Yakima River. A B e Cl e Teanaway E Campground l u Te m an 903 aw k a e y e r C Roslyn R R i v id e r g k e u E T a e a w n S C a w a y R o a d 84 Cle Elum 970 90 er iv R 903 a Y ki m a Miners dig up coal from the Roslyn Formation. D 97 Washington Geological Survey Photo Collection Modern (now to ~11 ka) Pleistocene (~11 ka to 2.4 Ma) Eocene (~34 to 58 Ma) ● Over 60 million tons of coal were mined from the rocks of river and stream deposits glacial drift and outwash: poorly upper Roslyn Formation: light-colored defined layers of boulders, sandstone; layers of coal common the upper Roslyn Formation between 1882 and 1963. An landslides middle estimated 240 million tons of coal remains, but it is currently cobbles, pebbles, sand, and silt; in upper section; contains fossil carried down valleys by glaciers lower leaves; formed in an ancient uneconomical to mine. coastal plain glacial lake deposits: well-defined Cle Elum–Roslyn coal field layers of sand, slit, and clay Teanaway Basalt: black to reddish (mined from 1882 to 1963) brown or yellow; often blocky with Miocene (~15.6 Ma) few layers; molten basalt filled campground ancient valleys Grande Ronde Basalt: well-defined A point of interest layers of dark gray to black Swauk Formation: light-colored 84 freeway exit number volcanic rock; forms flat-topped sandstone; thin layers of coal hills and steep slopes or cliffs www.dnr.wa.gov/geology fault—dotted where covered.