| Yakima Fold Belt | |
| Other Name: | Yakima fold-and-thrust belt |
| Map: | Washington |
| Relief: | yes |
| Mark: | City locator 17.svg |
| Location: | South-western part of Columbia Basin (Yakima, Kittitas, Klickitat, Benton, and Grant counties) |
| Coordinates: | 46.4°N -120.5°W |
| Type: | Fold and thrust belt |
The Yakima Fold Belt of south-central Washington, also called the Yakima fold-and-thrust belt, is an area of topographical folds (or wrinkles) raised by tectonic compression. It is a 14000km2 structural-tectonic sub province of the western Columbia Plateau Province resulting from complex and poorly understood regional tectonics. The folds are associated with geological faults whose seismic risk is of particular concern to the nuclear facilities at the Hanford Nuclear Reservation (immediately northwest of the Tri-Cities) and major dams on the Columbia and Snake Rivers.
circle 180 16 16 Lake Keecheluscircle 204 24 20 Lake Kachesscircle 224 34 16 Lake Cle Elumcircle 254 56 16 Cle Elumcircle 314 100 16 Ellensburgcircle 434 48 16 Quincycircle 480 24 16 Ephratacircle 522 76 20 Moses Lakecircle 506 92 20 Pot Holes Reservoircircle 538 140 16 Othellocircle 320 200 16 Yakimacircle 324 214 12 Union Gapcircle 570 326 16 Wallula Gapcircle 262 378 16 Goldendalecircle 212 434 16 The Dallescircle 156 406 16 Hood Riverpoly 1 30 12 32 12 46 1 46 Tacomapoly 510 264 558 264 558 292 510 292 Tri-Cities
circle 120 134 22 Mount Rainiercircle 56 294 22 Mount St. Helenscircle 164 288 22 Mount Adams
poly 374 14 386 6 394 16 382 24 Rock Island Damcircle 408 134 16 Wanapum Damcircle 418 184 16 Priest Rapids Damcircle 582 278 16 Ice Harbor Damcircle 502 354 16 McNary Damcircle 290 402 16 John Day Damcircle 224 422 16 The Dalles Damcircle 102 408 16 Bonneville Dam
poly 72 48 140 52 160 90 152 122 142 126 146 108 132 64 88 66 White River
poly 232 30 260 32 292 56 280 64 268 58 235 40 Cle Elum Ridgepoly 238 64 252 60 278 74 274 82 260 74 244 74 South Cle Elum Ridgepoly 224 80 242 82 286 104 306 106 378 144 380 160 298 118 272 118 232 100 Manastash Ridgepoly 282 122 300 124 382 172 422 188 442 190 436 198 420 196 404 192 380 190 314 142 296 140 280 128 Umtanum Ridgepoly 336 92 356 100 374 122 366 126 348 118 Boylston Mountainspoly 382 2 410 2 396 20 Badger Mountainpoly 404 22 422 2 478 2 470 30 406 32 Beezley Hillspoly 364 130 376 126 420 138 470 138 520 146 548 166 540 178 514 160 418 156 392 148 Saddle Mountainspoly 380 100 406 92 512 106 526 112 516 120 386 110 Frenchman Hillspoly 470 184 494 188 502 206 594 208 472 198 Gable Mountainpoly 250 124 266 126 284 148 290 158 278 158 254 142 Cleman Mountainpoly 322 182 344 178 380 192 404 194 452 212 446 222 416 210 382 216 336 200 Yakima Ridgepoly 210 166 352 150 268 162 246 176 226 174 Bethel Ridgepoly 252 194 272 182 310 190 306 198 276 196 360 204 Cowiche Mountainpoly 218 222 248 204 254 208 246 214 224 230
poly 72 1 186 1 640 336 640 386 418 212 316 190 Olympic–Wallowa Lineamentpoly 510 109 528 100 612 334 594 334
The topographical distinctness of the Yakima Folds (see the shaded-relief image) is due to their formation in a layer of lava flows and sedimentary deposits that have filled-in and generally smoothed the topographic surface of a large area of the Columbia Basin. The extent of these lava flows was limited to the west and north by the rising Cascade Mountains and the Wenatchee Mountains. The lava flows extend east well beyond this image, but the Yakima Folds do not. The northernmost fold seen here[1] (Frenchman Hills) ends at the Potholes Reservoir, another (Saddle Mountains) terminates just south of there, near the town of Othello (red circle). South of the Tri-Cities the rampart of the Horse Heaven Hills extends for a short distance past the Columbia River. The ends of these ridges mark the edge of a block of continental crust (part of the North American craton, indicated by the dashed orange line) that has resisted the tectonic compression that formed the ridges.
The southernmost ridge of the Yakima Fold Belt is the Columbia Hills on the north side of the Columbia River. The pattern of folding continues with the Dalles-Umatilla Syncline just south of the Columbia River, and further into Oregon with the Blue Mountains anticline, which approximately parallels the Klamath-Blue Mountain Lineament that marks the southeastern edge of Siletzia (see geological map, below).
The Yakima Fold Belt is also located on, and the orientation and spacing of some of the Folds influenced by, the Olympic–Wallowa Lineament (OWL), a broad zone of linear topographical features (dashed yellow line) extending from the Olympic Peninsula in northwestern Washington to the Wallowa Mountains in northeastern Oregon.
It is the central portion of the Olympic–Wallowa Lineament, referred to as the Cle Elum-Wallula deformed zone (CLEW), constising of a series of generally east-trending narrow asymmetrical anticlinal ridges and broad synclinal valleys formed by folding of Miocene Columbia River basalt flows and sediments. In most parts of the belt the folds have a north vergence (Columbia Hills' south vergence is an exception) with the steep limb typically faulted by imbricate thrust faults. Fold lengths range from 1 km to 100 km with wavelengths from several kilometers to 20 km.
A graben underlies nearly the entire Yakima Fold Belt and has been subsiding since Eocene time, and continues to sink at a slow rate.
A 2011 report found aeromagnetic, gravity, and paleoseismic evidence that the Yakima Fold Belt is linked to active Puget Sound faults.
Geodetic studies of the Oregon Rotation show that Oregon is rotating about a point somewhat south of Lewiston, Idaho compressing the Yakima fold an average of 3 millimeters per year, and the Washington Pacific coast about 7 millimeters per year.
Studies of the motion of the Yakima Fold Belt have been undertaken to evaluate seismic hazards at the Hanford Site.