Bedrock Geology of the Lake Tapps Quadrangle Pierce County Washington GEOLOGICAL SURVEY PROFESSIONAL PAPER 388-B Bedrock Geology of the Lake Tapps Quadrangle Pierce County Washington By LEONARD M. CARD, JR. GEOLOGIC STUDIES IN THE PUGET SOUND LOWLAND, WASHINGTON GEOLOGICAL SURVEY PROFESSIONAL PAPER 388-B A study of Tertiary sedimentary, volcanic, and intrusive rocks in the western foothills of the Cascade Range UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Page Abstract-___________________________ Bl Oligocene Series Continued Introduction. _______________________ 1 Intrusive rocks Continued Location, culture, and accessibility- 1 Latite___________________________________ B21 Purpose ________________________ 2 Miocene deposits.____________-___----__-_--__------ 22 Fieldwork and acknowledgments. __ 2 Description_ __________________________________ 22 Previous work.__________________ 3 Fossils and age________________-___-_-__---_---_ 23 General setting-_____________________ 3 Origin.______________________________________ 23 Drainage and relief. _____________ 3 Source__________---------------__-_--_---_---_- 24 Climate and vegetation._________. 4 Structure ______________________.._--__-.-----_------ 25 Regional geologic setting________ 4 Major folds________________----_-_____-_--_---_ 25 Stratigraphy ________________________ 4 Minor folds------------------------------------ 26 Eocene Series-_________-_-_-_-__--__ 5 Faults-,-_--_----_------------___-__----__ 26 Puget Group,___________________ 5 Origin of intense deformation in the Carbon River Carbonado Formation. _______ anticline. ____________________________________ 27 Northcraft Formation. _______ Age of deformation-___-________________-_-----_ 27 Spiketon Formation.________ 11 Economic geology________-___-_--________--__------ 29 Origin of the Puget Group.___ 12 Coal. _________________-_--_--_._____--___----- 29 Correlations. _______________ 13 Construction stone._____________________________ 29 Oligocene Series.____________________ 15 Clay deposits---------------------------------- 30 Ohanapecosh Formation,_________ 15 Oil and gas____________________________________ 30 Intrusive rocks.____-____----____ 18 Geology of a potential damsite in the Carbon Gorge. _ 30 Quartz diabase. 18 Suitability as a damsite_ _____________________ 31 Hornblende dacite porphyry. 20 References cited-_______-____------________--_-_---- 32 Pyroxene andesite_________ 21 ILLUSTRATIONS Page PLATE 1. Map and sections showing bedrock geology and structure of part of the Lake Tapps quadrangle._____ _ _ _ In pocket 2. Geologic map and sections of a potential damsite at Fairfax Bridge._________________________________ In pocket FIGURE 1. Map showing location of mapped area____________ ______........____________________-________--_-_-- B2 2. Photograph of ripple-marked sandstone in the Carbonado Formation.-__________________________-------_ 6 3. Cumulative curves of sandstone samples-__________________-_________--__---------------_------------ 7 4-6. Photographs: 4. Contact of westward-dipping mudflow breccia at base of the Northcraft Formation______-__-----___ 9 5. Volcanic mudflow breccia in Northcraft Formation.____________________--__-----_____-_-------- 9 6. Concentration of boulders in basal part of a volcanic mudflow breccia____-__-_-----___-_--_------- 10 7. Chart showing relation of Puget Group to other Tertiary rocks_________-_-___-_-_-------.----_--_------- 14 8. Sketch map showing relation of Puget Group to Ohanapecosh Formation.______--____--_-_____-_---_--__ 15 9. Photomicrograph of volcanic sandstone from the Ohanapecosh Formation-_____-_______----________---___ 16 10. Photomicrograph of tuff from the Ohanapecosh Formation.__________________________---._--------__---- 17 11. Photograph showing xenoliths of andesite in hornblende dacite porphyry.________________________________ 20 12. Photomicrograph of hornblende dacite porphyry.____________________-____-__-_---_-_--_--------_---__ 20 13. Photomicrograph of latite that crops out in a roadcut-__________________-_-__-_-__-_-_-_____-----__--- 22 14. Diagrammatic cross sections showing hypothetical sequence of structural development in the Carbon River anticline-____________________________________________________________________________________ 28 TABLE Page TABLE 1. Rapid chemical analyses of rocks in the Lake Tapps quadrangle. _________________-_-------_------------ B24 in GEOLOGIC STUDIES IN THE PUGET SOUND LOWLAND, WASHINGTON BEDROCK GEOLOGY OF THE LAKE TAPPS QUADRANGLE, PIERCE COUNTY, WASHINGTON By LEONARD M. GARD, JR. ABSTRACT Miocene age were deposited on an uneven surface of Eocene Bedrock crops out in an area of about 100 square miles in the rocks. The alluvium and mudflows were probably derived from south half of the Lake Tapps quadrangle, Washington, in the an area in the Cascade Range where a granodiorite batholith western foothills of the Cascade Range about 20 miles east of may have broken through to the surface, causing explosive Tacoma. Bedrock consist of (a) more than 11,000 feet of Eocene volcanism. The Miocene deposits probably are equivalent to and Oligocene sedimentary and volcanic rocks of the Puget part of the Ellensburg Formation on the east flank of the Group and the lower part of the Ohanapecosh Formation, (b) Cascades. intrusive rocks of probable Oligocene or Miocene age, and (c) East-trending normal faults of small displacement have offset thin semiconsolidated sedimentary deposits of Miocene age. the Miocene and older rocks. Rocks of the Puget Group are more than 9,000 feet thick and Small intrusions of igneous rock of probable Oligocene or are divided, in ascending order, into the Carbonado, Northcraft, Miocene age occur as dikes, sills, and plugs in rocks of Eocene and Spiketon Formations. The Carbonado and Spiketon Forma­ and Oligocene age. The finer grained intrusive rocks are tions consist of arkosic .sandstone, siltstone, shale, and coal de­ andesite and latite, and the coarser grained rocks are quartz posited in an environment of brackish-water streams and deltas diabase and hornblende dacite porphyry. adjacent to a marine embayment west of the quadrangle. These Bituminous coal has been mined from the Puget Group since two formations had a common source to the east and are in­ 1874. Most of the higher grade coal was taken from the distinguishable except where the Northcraft Formation is pres­ Carbonado Formation, which also provided the best coking ent between them. The Northcraft in the Lake Tapps quadrangle coal on the west coast. Little mining is being done now, although consists of a wedge of andesitic volcanic breccias derived from resources estimated to be 362 million tons still remain. Other areas to the southwest. known resources in the bedrock of the quadrangle are clay, and The Ohanapecosh Formation conformably overlies the Puget stone for building construction, riprap, and road metal. Group and is composed of sedimentary rocks of volcanic detritus and interbedded pyroclastic rocks. This volcanic debris origi­ INTRODUCTION nated somewhere east of the quadrangle. Only 2,500 feet of LOCATION, CULTURE, AND ACCESSIBILITY Ohanapecosh rock crops out in the quadrangle, although more than 10,000 feet is presumably present in the Cascade Range The Lake Tapps 15-minute quadrangle is in Pierce to the east. and King Counties southeast of Tacoma in western During Oligocene and Miocene time the Eocene and Oligocene Washington (fig. 1). The quadrangle includes four rocks were folded into the Carbon River anticline, which trends and plunges north-northwest and can be traced from Burnett 71/2-minute quadrangles: (clockwise from the north­ south to the Nisqually River. North of Burnett the anticline is west corner) Simmer, Buckley, Wilkeson, and Orting. concealed by surflcial deposits. Along the core of the anticline Bedrock crops out in the last three quadrangles; topo­ are several smaller tightly folded anticlines and synclines whose graphic maps of the Wilkeson and parts of the Buckley trends parallel that of the major structure. All the folds have and Orting quadrangles served as the base for the been broken by high-angle (chiefly reverse) faults that parallel the fold axes and that may have as much as 1,000 feet of dis­ geologic map (pi. 1). placement. Dips in the core of the Carbon River anticline range The largest communities in these three quadrangles from 0° to 90° and average about 60°. On the west limb of the (and their populations as of 1960) are Buckley (3,538), anticline the Northcraft Formation is more than 2,000 feet thick ; Orting (2,697), Carbonado (424), Wilkeson (412), on the east limb its maximum thickness is only 200 feet. Erosion and Burnett (100). The last three towns, which owe their may have removed the overlying Spiketon Formation from the west limb. inception to the coal-mining industry, have slowly The Carbon River anticline is believed to have resulted from dwindled in population since the mid-thirties, when east-west lateral compression acting on Carbonado rocks be­ most of the mines shut down. tween a buttress of thick downwarped Ohanapecosh Formation Sites of several abandoned coal-mining towns are now to the east and the competent Northcraft Formation to the west. Following Oligocene or early Miocene uplift and erosion, marked by a few buildings