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Haystack Dam |
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Statistics |
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Power Generation Narration
Geology Bedrock at the damsite was mapped as the John Day Formation. This mapping indicates the dam is a member of the formation consisting of rhyolite, ash-flow sheets, bedded, welded and lapilli tuffs with interbedded tuffaceous sedimentary rock. The implied source area for the volcanic material is Juniper Butte; a rhyolite dome with associated flows located two miles southwest of the dam. Robinson infers a north 75-degree trending fault one half mile south of Haystack Dam. The fault displaces John Day Formation and the underlying Clarno Formation but does not cut the younger Madras Formation surrounding the butte and overlapping the older formation. Surficial deposits on the valley floor along the axis of the dam ranged from 0 to 24 feet in depth. These deposits were alluviums, consisting of silty sand, coarse sand, clayey sand and gravel. Toward the left abutment the overburden deposits were alluvium and talus and near the base of the slope about 30 feet thick. Bedrock under the surficial deposits in the valley consisted of rhyolite and tuff and was exposed at the surface near the top of both abutments. Links | Recreation | | Dams Located by State | USBR Oregon Dams | Pacific Northwest Region Dams || Owner: Bureau of Reclamation, Lower Columbia Area Office, 1201 NE Lloyd Boulevard Suite 750, Portland, OR 97232-1295, Phone: 503-872-2795, Fax: 503-872-2797 | Operator: North Unit Irrigation District,
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