Geological Survey Bulletin 581—B Oil and Gas in the Western Part of the Olympic Peninsula, Washington

ROCKS EXPOSED ALONG CLEARWATER RIVER WEST OF THE OLYMPIC NATIONAL FOREST.

The strata exposed along Clearwater River west of the Olympic National Forest probably all belong to the "supposed Cretaceous" formation and are better and more continuously exposed than the rocks of any other part of the area examined. (See Pl. II, p. 78.) Although these beds are well exposed, yet the unusual number of folds and small faults makes the interpretation of the structure very difficult. The Pleistocene beds of clay, sand, and conglomerate are exposed at only a few places. In fact Clearwater River runs from the western boundary of the Olympic National Forest to a point about one-fourth of a mile north of Clearwater post office, through a comparatively narrow canyon of the older rocks, whose walls attain a maximum height of 200 feet.

At location A, about one-half mile above the mouth of Clearwater River, on the east side of the stream, there is an exposure of yellowish-brown sandstone and yellowish gravel very poorly consolidated. These beds lie practically flat and unquestionably can be correlated with the beds of Pleistocene age in other parts of the field. Soft, yellowish-brown sandstone is exposed at location B in the northern part of sec. 30, T. 24 N., R. 12 W., on the west side of the river. The beds here are medium bedded, dip 37° NE., and strike N 30° W. At location C, about one-fourth of a mile farther north, the "flaglike" beds, consisting of thin-bedded sandstone alternating with sandy shale, outcrop on the west side of the river. They dip 73° NW. and strike N. 40° E. The total thickness of the beds exposed here is approximately 800 feet. At the north end of this exposure the strata dip 71° NW. and strike N. 35°-40° E. The "flaglike" beds of alternating sandstone and sandy shale are exposed at location D, just below the mouth of Hurst Creek, and also for 300 or 400 feet up that stream, where the strata dip 74° E. and strike N. 5°-10° E. At location E, on the west side of Clearwater River, about one-half mile upstream from the mouth of Hurst Creek, beds of hard dark-gray resistant sandstone about 500 feet thick are exposed. The upper part (stratigraphically) of this exposure is not distinctly bedded, so that dip and strike readings are not reliable. The lower portion of the beds dips 68° W. and strikes N. 5°-10° E. At location F, on the east side of the river, about 100 feet of "supposed Cretaceous" sandstone dips 49° NW. and strikes N. 55° E. At location G, at the west end of the big bend in the river in the SE. 1/4 sec. 12, T. 24 N., R. 13 W., the "flaglike" beds, which dip 60° E. and strike N. 5° W., are also exposed. The strata exposed at location H, on the east side of Clearwater River, about three-fourths of a mile east of location G, consist of about 250 feet of the "flaglike" beds, which are overlain unconformably by fairly well consolidated Pleistocene conglomerate at least 100 feet thick. The "flaglike" beds are inclined 30° NE. and strike N. 45° W. The striking differences noted here in angle of dip and in direction of strike are due to abrupt flexures and in places possibly to small faults. At one locality a short distance upstream from location H the beds dip 29° NW. and strike 18° E. The same beds 150 feet farther upstream dip 39° SE. and strike N. 30° E. and at location I, 200 feet farther upstream, the dip is 36° SE. and the strike is N. 65° E. The "flaglike" beds at this place consist of about 60 per cent of sandstone and 40 per cent of shale in beds 2 or 3 inches in greatest thickness. About 300 feet farther upstream from location I the same beds stand vertical and strike N. 55° E.

At location J, on the east side of Clearwater River and about one-third of a mile north of location I, beds of sandy shale dip about 66° NE. and strike N. 25° W. At location K, at the west end of a prominent bend, approximately in the SE. 1/4 sec. 1, T. 24 N., R. 13 W., the sandstone and shale beds of the same formation as that described above, as far as can be ascertained, dip 55° NE. and strike N. 60° W. The strata are much disturbed by folds and small faults, as the following dip and strike readings show. At a point 25 feet downstream from location K the beds dip 60° SW. and strike N. 20° W. The fault line separating the points where these two last-mentioned dip and strike readings were taken is very distinct. About 1,000 feet farther downstream the "flaglike" "supposed Cretaceous" beds stand vertical and strike N. 20° W. A few hundred feet farther downstream and on the opposite side of the river beds of massive, much broken sandy shale are exposed, but it was not possible to measure dip and strike readings on these beds. At location L, about 1 mile upstream from location K, the "flaglike" beds dip 87° S. and strike N. 85° W. A short distance downstream from this place the same beds dip 58° SE. and strike N. 30° E. At location M, on th south side of the river, in the northeastern part of sec. 6, T. 24 N., R. 12 W., and 600 or 800 feet northeast of location L, the "flaglike" beds dip 67° SE. and strike N. 70° E. At location N, on the east side of the river and about one-half mile farther north, beds of gray sandstone, which alternate with thin beds of shale, are exposed for a short distance. The dip is 67° E. and the strike N. 10° W. Exposures are fairly good on the east side of the river from location N southward for one-fourth to one-half mile. Several hundred feet of strata are well exposed in the vicinity of location O, in the northern part of sec. 32, T. 25 N., R. 12 W. At the western end of this exposure the beds, which dip 56° NW. and strike N. 30° E., consist of dark-bluish sandy shale and several hundred feet of "flaglike" beds of alternating sandstone and shale. Many of the joints of these strata are filed with iron-stained calcite. A short distance east of location O beds of gray sandstone, overlain by a few hundred feet of dark-bluish sandy shale, dip 65° W. and strike north. The beds upstream from location O have a brownish tinge, whereas those downstream are bluish-black. From the mouth of Elkhorn Creek, which joins Clearwater River in the NE. 1/4 sec. 32, to location O the river flows through a narrow canyon in the walls of which the "flag-like" beds, together with some dark shale, are well exposed. On the south side of the river in this canyon the beds in places stand almost vertical. At location P, just above the mouth of Elkhorn Creek, strata of similar character that dip 42° NE. and strike N. 20° W. are well exposed for a short distance. A little farther upstream, at location Q, approximately in the SE. 1/4 sec. 29, T. 25 N., R. 12 W., sandstone beds dip 51° SE. and strike N. 20° E. At location R, on the west side of Clearwater River, about one-half mile northeast of location O, beds of sandy shale that dip 40° SE. and strike N. 25° E. are exposed for 300 or 400 yards. A few hundred feet southwest of location R the strata dip 45° NE. and strike N. 30° W. This dip and strike reading is not so reliable as the readings taken at locations Q and R. At the mouth of Shale Creek (location 5) about 6 feet of sandstone containing calcite in the joints, overlain by bluish-black shale containing hard calcareous nodules, is exposed. The beds at this place dip 63° SE. and strike N. 55° E. About 500 or 600 feet north of the mouth of Shale Creek gray hard fine-grained shaly sandstone is exposed on the east side of Clearwater River. The strata both overlying and underlying this sandstone are poorly exposed, but seemingly consist of dark-bluish sandy shale interbedded with shaly sandstone. They dip 53° NE. and strike N. 45° W.

An unusually long and steep rapid, known locally as the "Skukemchuck," is situated a few hundred feet upstream from the mouth of Shale Creek. At location T, on the west side of the river, one-third of a mile upstream from location S, about 300 feet of yellowish-gray sandstone and bluish-yellow sandy shale are exposed. In both directions from location T, for at least one-fourth of a mile, dark-bluish sandy shale is exposed in the river banks. These beds are cut by joints and fracture planes which in many places are filled with calcite. The rocks are so much broken by small faults that within a distance of 200 feet beds may be found flat-lying, almost vertical, and dipping 45°, all striking in different directions. At location U, on the east side of Clearwater River and just below the mouth of Miller Creek, there is an outcrop of dark-brown to black clay shale, in which the surfaces of joints and fractures show slickensides. At the mouth of Miller Creek on the north side of the river there is a fairly good outcrop of yellowish-gray sandstone. These beds are so deformed that reliable readings of dip and strike could not be made. At location V, on the south side of the river and about one-half mile farther upstream, the "flaglike" beds consist of soft, dark thin-bedded sandy shale and sandstone, which dip 72° SE. and strike N. 60° E. At the upper end of the outcrop near the bend of the river the beds seem to be overturned. The dip is 89° NW. and the strike N. 65° E. Approximately 300 feet of shale and shaly sandstone outcrop at this easternmost exposure.

On the west side of Clearwater River, beginning a short distance north of Giberson's house, situated in the NE. 1/4 sec. 27, T. 25 N., R. 12 W., sandstone and sandy shale are exposed almost continuously upstream to the mouth of Christmas Creek. At location W, which is on the west side of the river and about 100 yards below the mouth of Christmas Creek, beds of bluish sandy clay, which dip 33° N. and strike N. 80° W., are exposed. Many small faults and folds were observed here. At location X, about one-half mile south, slightly east of location W, beds of dark sandy shale are exposed on the south side of the river. These beds dip 59° E. and strike N. 10° E. About 100 feet upstream from location X the rocks are cut by a small fault and about 300 feet farther up the river the same beds dip 48° E. and strike N. 10°-15° E. Between the fault and the point where the last dip and strike readings were measured, the strata are much contorted and strike more nearly east. At location Y, on the south side of Clearwater River, approximately in the NE. 1/4 NW. 1/4 sec. 26, T. 25 N., R. 12 W., beds of sandstone and sandy shale that dip 15°-20° E. and strike N. 10°-15° E. are fairly well exposed for a short distance. Some of these beds are "flaglike" in appearance and are similar to those mentioned as occurring at other places along this river. About 500 feet farther up the river "flaglike" beds that dip 24° SE. and strike N. 25° E. are well exposed and are overlain unconformably by poorly consolidated conglomerate of Pleistocene age. At location Z, situated near a bend in Clearwater River, about 1-1/4 miles directly west of the Olympic National Forest boundary, beds of bluish sandy clay and slightly consolidated conglomerate of Pleistocene age are exposed, but the bedding is so indistinct that dip and strike readings could not be obtained. At location AA, on the south side of Clearwater River, in the NE. 1/4 sec. 26, T. 25 N., R. 12 W., beds of dark-bluish sandy shale, alternating with yellowish-gray medium to thin bedded sandstone, are exposed. The dip at this place is 67° S. and the strike is approximately east. At location BB, in the northern part of sec. 25, T. 25 N., R. 12 W., similar beds of sandstone and sandy shale, containing probably a little more shale than the beds at location AA, dip 85° SE. and strike N. 40° E. At location CC, on the north side of the river a short distance west of the forest reserve line, the same beds, dipping 63° NW. and striking N. 45° E., are also exposed. The "flaglike" beds are exposed fairly well at location DD, on the north side of the river, presumably just west of the boundary of the Olympic National Forest. Dip readings on these beds range from 40° NW. to vertical and the strike is N. 65° E. At location EE, at the bend of the river a short distance above the mouth of Deception Creek, which is the easternmost point visited by the writer during the traverse of this river, beds of sandstone with a little intercalated shale are exposed on the south and east sides of the river. The beds stand almost vertical and strike N. 65° E.

Practically all the rocks exposed along Clearwater River, with the exception of those outcropping at locations A and Z, are believed to belong to the "supposed Cretaceous" formation.

The beds of bluish sandy clay and poorly consolidated sand and conglomerate exposed at locations A and Z and overlying the "supposed Cretaceous" at locations H and Y are of Pleistocene age. The rocks on the uplands are concealed by a thick mantle of soil, hill wash, and talus.