The structure of the area represented on Plate II (p. 78) is characterized by a prominent anticline or possibly a monocline, the axis of which is situated some distance out in the ocean, extending in a general north-south direction in places, turning slightly to the northwest. The east flank of this anticline, which underlies the area under consideration, is crossed almost at right angles to its strike by several smaller anticlines and synclines. The general structure is indicated on the accompanying map (Pl. II) by dip and strike symbols, which almost invariably show that the rocks dip in general toward the east and strike in a north or northwest direction. The minor anticlines and domelike structures are also shown by dip symbols.
One of the most prominent of these minor anticlines crosses Queets River about 2-1/2 miles from the coast, extending northeast and southwest through the eastern part of sec. 35 and the northwestern part of sec. 36, T. 24 N., R. 13 W. The dips of the rocks on Clearwater River, a mile or more north of the present site of Clearwater post office, indicate that the same anticline that crosses Queets River near its mouth extends to that locality, but there it seems to be somewhat narrower than it is near the mouth of Queets River. A study of the dips and strikes farther up Clearwater River does not indicate that it continues for a great distance north of sec. 18, T. 24 N., R. 12 W. The writer is unaware of any gas or oil vents along this anticline.
There is evidence of another prominent, although narrow, anticline extending in the same general direction on the coast at the mouth of Cedar Creek, about 3-1/2 miles southeast of the mouth of Hoh River. This anticline seems to cross Hoh River a short distance east of Hoh post office. It is interesting to note that the Lacy seep, situated in the NW. 1/4 sec. 11, T. 26 N., R. 13 W., is nearly on the projected axis of this anticline. "Smell mud" is plentiful on the coast near the mouth of Cedar Creek.
Another prominent anticline in "supposed Cretaceous" rocks cuts the coast just south of Hoh Head and like the two anticlines just discussed extends in a northeast direction. No evidence is at hand regarding its extent inland. The Jefferson Oil Co.'s seep and well are situated near the crest of this anticline. Oil-saturated rock is not known to exist along the coast on the upfold, but a little farther south, near location Z, it is plentiful.
As was pointed out by Arnold, the Queniult formation, which outcrops on both sides of the mouth of Queniult River along the coast for 2 miles, occupies a broad syncline. This syncline, to judge from dips and strikes along the coast and about 2 miles above the mouth of Queniult River, also trends in a northeast-southwest direction.
The structure of the beds of Pleistocene age is very simple. In most places they lie practically horizontal. At those localities in which these strata are somewhat inclined their disturbance is undoubtedly of recent date and is due probably to landslides and slumps, which in some places have produced buckling.
Evidences of other small anticlines are pointed out below in the description of the structure by districts. The description of the Pleistocene beds will be omitted in these detailed descriptions, as their Structure has nothing to do with the accumulation of oil and gas.
Between locations A and B there are no exposures of the older rocks except in the vicinity of location A, near Copalis Rock, where, as has been stated above, reliable dip and strike readings could not be obtained. Between locations D and E, in the vicinity of Point Grenville, much faulting has taken place in what is believed to be the old metamorphic rocks. Dip and strike readings and measurements of the inclination and direction of fault planes differ so widely that the more prominent features of the structure in this locality can not be shown on a map of the scale of Plate II. The principal fact of interest is, however, that between locations D and E lies an upfaulted block of metamorphic rocks, which is very much faulted and folded within itself.
The Queniult formation exposed between locations E and H, in the vicinity of the mouth of Queniult River, is in general a broad syncline, the axis of which extends in a northeast direction and which cuts the coast a short distance south of the mouth of Queniult River. It is doubtful if this formation has any important relation to oil or gas that may underlie these strata in the "supposed Cretaceous" beds. Between locations H and I, along the coast, there is evidence again of a comparatively narrow upfaulted block of "supposed Cretaceous" rocks. Northward from location I to the mouth of Raft River the "supposed Cretaceous" rocks strike in general north slightly east and dip east in almost every locality. At the mouth of Raft River a fairly reliable measurement shows that the beds dip about 53° NW. and strike N. 25° E. for a short distance. This narrow anticline is associated with "smell mud" along the coast, as is shown on Plate II (p. 78).
Flat-lying beds of Pleistocene age occupy the coast from location O to location Q with the exception of a very small area at the mouth of Kalaloch Creek. Northward from location Q to a point a short distance south of the mouth of Cedar Creek the general strike of the strata ranges from north to N. 18° E., the dip being generally eastward. A small anticline, described above, breaks the monotony of the general eastward dip for about one-half mile north of the mouth of Cedar Creek, north of which point the older strata are entirely covered for some distance by flat-lying Pleistocene beds. In the vicinity of the mouth of Hoh River and to the northwest as far as location EE, about 1 mile north of Hoh Head, the strata are much disturbed by northeast-southwest anticlines and some still smaller folds and faults. Near the mouth of Hoh River there is evidence of an elongated dome extending in general east and west. Faulting has disturbed this structure at location A, on Hoh River. A mile or more northwest of location Z, on the coast, the prominent northeast-southwest anticline on which the Jefferson Oil Co.'s seep and well are situated dominates the structure. North of Hoh Head there are also indications of a minor anticline extending in a northwest direction, as suggested by a dip of 45° SW. and a strike of N. 65° W. at location DD, whereas there is a dip of 60° E. and a strike of N. 10° W. at location EE.
The general dip of the strata along Humptulips River and the east fork of the same river between the village of Humptulips and location I, about 4 miles southeast of East Fork dam, is to the east. Beds exposed at location J, a short distance west of the contact between the sedimentary and igneous rocks, have a steep dip to the west. The dip and strike symbols on Plate II show the details of structure along Humptulips River better than any written description. The structure of the almost flat-lying beds of Pleistocene age on Camp No. 2 and Stevens creeks needs no further explanation than that shown on the map (Pl. II, p. 78) in addition to what has already been stated under the heading "General features" (p. 74).
The beds exposed along the lower course of Moclips River outcrop in an anticline which trends in a northwest-southeast direction. The extent of this anticline in either direction is not known on account of the thick cover of Pleistocene beds, and for that reason the position and direction of the axis are shown only near the stream.
The description of the structure of the rocks exposed along Queniult River and Queniult Lake will necessarily be brief because the beds exposed in this part of the field are principally of Pleistocene age and in general are flat-lying. The rocks in the vicinity of Higley's hotel, in sec. 8, T. 23 N., R. 9 W., at Onion Rock, and the two exposures farther west presumably belong to the "old metamorphic series," as do also the rocks exposed at Burnt Hill in secs. 1 and 12, T. 22 N., R. 11 W. As stated before in this report, it is believed that the rocks exposed at Burnt Hill are greenstone, whereas those in the vicinity of Higley's hotel on the north side of the lake, which in places seem to stand almost vertical, are believed to be in part sedimentary.
The strata outcropping at locations A, B, and D, near the mouth of Queniult River, and at location I, about 10 miles from the coast, dip in general to the east. They are broken in places, as has been stated before in the detailed description of location D, on page 30. Without doubt the beds at locations A, B, and D belong to the Queniult formation and possibly those outcropping at location I also. There is a probability, however, that the rocks at location I may be "supposed Cretaceous," in which case a fault or fold must exist to the southwest and west of this exposure. If it is an upfold the axis of the anticline or monocline, on the north flank of which this outcrop is situated, must necessarily lie to the south of this locality, but no information is at hand regarding its exact position.
The outcrops of rock on which dip and strike readings were measured along Queets and Clearwater rivers and the lower courses of Salmon River and Matheny and Sams creeks are much more numerous than are the exposures in any of the other regions examined. The prevailing dip of the rocks, as a glance at the dip and strike symbols on Plate II indicates, is in general to the east. However, at localities where faulting and folding have disturbed the strata, the strike of the beds as well as the direction of dip differs considerably. As stated on page 74, the principal anticline in this basin seems to cross Queets River about 2-1/2 miles above its mouth. The evidence of an anticline on Clearwater River in the vicinity of locations D and E is fairly conclusive, but it is questionable if the anticline noted near the mouth of Queets River and the one on Clearwater River in the vicinity of locations D and E are the same, and it would be unwise to definitely correlate them. A correlation, however, is suggested on account of the relative positions of these two sections of anticlines, as the strike of the rocks near the mouth of Queets River at locations A, B, and C shows that it would cross Clearwater River, if continued in the same direction, at approximately the posiion where the anticline on Clearwater River exists. More detailed work along Elk Creek and tributaries of Elk Creek in secs. 24 and 25, T. 24 N., R. 13 W., would undoubtedly furnish conclusive evidence regarding this point if these streams have eroded through the Pleistocene cover. Between location L on Queets River and location D on Sams Creek, a distance of about 14 miles as the river runs, no outcrops of the "supposed Cretaceous" or Tertiary formations are exposed. This distance is sufficient for several small narrow anticlines, but no evidence is at hand, even taking into consideration the beds exposed in the canyon of Matheny Creek, that there are any such favorable structures for the accumulation of oil or gas. As noted on page 63, the prevailing dip of the rocks in Matheny Creek canyon is to the east, which corresponds exactly with the prevailing eastward dip of the rocks along all the principal streams in the area represented by Plate II.
Dip and strike measurements taken in Salmon River canyon between locations A and E suggest the existence of an elongated dome or anticline, which are favorable structures for the accumulation of oil and gas. As the strata here are broken by minor faults, and as the same beds on Queets River about a mile to the north have persistent eastward dips, it is very questionable if the structure here is really favorable.
Although the dip and strike of the rocks along Clearwater River indicate that the structure is very complex, yet the more reliable measurements show that the rocks have a general eastward dip and that prominent anticlines are absent. Wherever westward dips occur they are usually due to the presence of faults and folds which undoubtedly do not extend to a great depth below the surface and hence would have but little effect in constituting reservoirs for the accumulation of oil and gas.
Dip and strike readings measured at the mouth of Hoh River, although very meager, suggest that a narrow anticline or possibly a small dome is situated here. This structure apparently does not extend far inland or far north or south from the mouth of Hoh River. About one-half mile southeast of Hoh post office "supposed Cretaceous" beds strike approximately N. 25° E. and dip about 75° NW. At the mouth of Cedar Creek there is evidence of a comparatively narrow anticline which has the same general trend. The axis of this anticline projected inland from the coast would cross the river near the point where the strata were measured in sec. 21, T. 26 N., R. 13 W., and if projected still farther north would lie near the Lacy seep. The position of the axis of the anticline north of Hoh River as above indicated is only approximate, but it seems that this assumption is fairly reasonable. Just east of Elliott's ranch the dip and strike readings indicate the existence of a small anticline which trends in a general northwest-southeast direction. The rocks are faulted slightly and the apparent anticline may not constitute a favorable structure. The rocks farther up Hoh River dip in general to the east, as they do along Queets and Clearwater rivers. The structure of the rocks exposed at the conspicuous canyon on Hoh River, at location I and to the west, and those outcropping at location K, southeast of Schmidt's house, on the south side of Hoh River, suggest that a northwest-southeast anticline may extend through this general region, the axis of which may cross the river in the vicinity of the gas vent reported by Billy Snell at location J, on the north side of Hoh River, approximately in the center of sec. 26, T. 27 N., R. 12 W. The rocks exposed at locations L and M, about a mile west of the Devils Mush Pot, near Spruce post office, have a general eastward dip, which suggests that this gas, if it is related structurally to the rocks exposed at locations L and M, must be escaping at some distance down the east flank of an anticline, the main axis of which may cross the river in the vicinity of location J, at the point where gas is escaping near Billy Snell's place.
Very little information regarding structure was obtained in this locality. As noted by the dip and strike symbols at locations A, B, C, D, and E, on and near Bogachiel River, and location A on Calawa River, about 2-1/2 miles northeast of Forks, the prevailing dip of the rocks is to the east, as at nearly all other localities in this field. Most of the points where the readings were taken are so widely separated that there is room, for one or more small anticlines to be present in the intervening space, but the writer has no evidence of their existence. Further detailed work along these streams and the streams to the north will undoubtedly yield valuable information regarding the position of any anticlines that may be present.
In regions where the strata are saturated with water ("wet"), as is the case in this field, oil and gas collect usually under anticlines or domes that are capped by some impervious stratum. On the other hand, in regions where the strata are comparatively "dry" the oil tends to collect in synclines or basins. The principle on which this action takes place is quite simple. Wherever open porous rocks contain water and oil disseminated through the mass there is a tendency for the water, being the heavier, to collect below and thus force the oil to occupy a position above it. If, however, the rocks are thoroughly saturated, there will be a general migration of the globules of oil upward through the strata until they reach the surface of the earth or until their progress is stopped by the presence of rocks like clay, shale, and dense sandstone, which are almost impervious to oil. If the porous stratum and the impervious cover are flat-lying probably there will be no large accumulation of oil, but if they are inclined slightly the oil will continue to migrate up the rise at or near the base of the impervious stratum until it reaches the upper limit of water saturation, or the surface of the earth and escapes in an oil spring or seep. If the structure is that of a dome or anticline the oil will collect in the porous rock directly underlying the impervious cap in the top of the anticline (except where gas is associated with the oil, in which case the gas will occupy the highest position) and remain there until it can escape to the surface through natural vents, such as seeps and fault planes, or artificial openings (drill holes). It is also true that if oil and gas are associated in the same rocks, as is usually the case, the gas, being lighter than the oil, will naturally occupy the crest of the anticline or apex of the dome underlying the impervious stratum. If the rocks are "dry" the disseminated oil particles acted upon by the force of gravity tend to migrate downward. If the structure is that of a syncline or basin underlain by an impervious stratum the oil will collect in the depression.
In this discussion the simplest condition, that in which the rock containing the oil is a homogeneous mass overlain or underlain by a stratum impervious to oil, is assumed. It is believed that where the conditions are more complex, as where the oil is included in a shale or compact thin sandstone containing lenses of coarser sandy material and the rocks are fairly saturated with water, the oil will be forced into the rock whose pore spaces are larger, owing to the differential capillary attraction of water and oil.
Last Updated: 28-Mar-2006