Long thin packets of structurally disrupted rocks in the eastern core of the Olympic Mountains mostly top eastward, but the overall age of the rocks decreases westward, suggesting early folding around subhorizontal axes with imbricate thrusting or imbricate thrusting alone. Continued east-west compression overturned beds eastward, bending the packets into an arc within the horseshoe bend of the Crescent Formation, a foldlike structure that formed as the core rocks were imbricated or was extant from the original arcuate distribution of basaltic seamounts. In the western part of the eastern core, secondary structures (B elements) (mostly small-scale folds) developed parallel to the steep axis of the fold of the basaltic horseshoe; in the southern part of the core, the rock packets were sheared off beneath the basalts on the south limb of the horseshoe bend. Later shear folding on a cleavage fan oriented parallel to a north-northwesttrending subhorizontal kinematic axis rotated B elements (folds) formed earlier, producing widespread late pencil structures, in part centripetal to the basaltic horseshoe, where the late cleavage intersected earlier deformed bedding and cleavage. This late folding produced a domelike structure extended asymmetrically eastward. The complex structure of the core rocks is consistent with current models of accretionary prisms in subduction zones and developed its form as the thick mass of volcanic rocks ofthe Crescent Formation to the east resisted the eastward movement of the accreted sedimentary prism.

QeEOLIAN DEPOSITS (HOLOCENE)-Well-sorted loose sand deflated from Columbia River floodplain that is now drowned behind dams Qb BOG DEPOSITS (HOLOCENE)-Peat and alluvium. Poorly drained and at least intermittently wet. Grades into unit Qa Qt TALUS DEPOSITS (HOLOCENE)-Nonsorted angular boulder gravel to boulder diamicton. At lower altitudes only arbitrarily distinguished from unit Oa. At higher altitudes in western part of quadrangle includes Holocene moraines, rock glaciers, and protalus ramparts LANDSLIDE DEPOSITS -Consist of: Qlsi Incipient blockslides (Holocene)-Large nonrotated mass of bedrock extensively crevassed as a result of slight movement toward nearby free faces. Crevasse -arrow symbol (not in digital coverage) shows direction of movement Qls Landslides (Holocene and Pleistocene)-Diamicton of angular clasts of bedrock and surficial deposits derived from upslope. Locally includes rotated blockslides. Arrows (not in digital coverage) denote downslope direction Qs ALLUVIUM (HOLOCENE AND PLEISTOCENE)-Moderately sorted cobble gravel along rivers grading to poorly sorted gravelly sand on small-tributary fans; as mapped, includes some material in fans similar to unit Qt Ql LOESS (HOLOCENE AND PLEISTOCENE)-Slightly compacted well-sorted silt. In places below edge of Columbia Plateau grades into unit Qe Qr REGOLITH (HOLOCENE AND PLEISTOCENE)-Slightly compacted to loose silt, diamictite, and soils. Extensive and thick on upland surfaces north and northwest of Columbia River. Includes considerable loess and weathering debris. Mostly mapped on basis of gentle ridgetop topography; contacts approximate GLACIAL DRIFT AND RELATED DEPOSITS Qgd GLACIAL DRIFT (PLEISTOCENE)-Ranges from till in uplands and upvalley areas t o gravelly outwash on broad valley floors. In lower Chelan Valley and in large valleys of Wenatchee drainage east of Lake Wenatchee, outwash gravel is interbedded with till and minor lacustrine sediment; in these areas gravel fraction is cognate with unit Qtg. Mostly last-glacial deposit, but in some places passes upslope into older, weathered drift. Conspicuous, large, sharp-crested moraines distinguished by dot-dash pattern

thanks to Carl Wentworth, who, no matter how busy, always answered questions about Alacarte. GENERAL GEOLOGYRocks in the Mount Baker quadrangle represent almost all the geologic events recorded in the entire North Cascades:(1) pre-mid-Cretaceous assembly of Mesozoic and Paleozoic terranes that have different paleogeographic origins and structural and metamorphic histories (Tabor and others, 1989; , (2) mid-Cretaceous to Late Cretaceous thickening by thrusting and pluton accumulation (

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