Geologic Map of the Sandpoint 30' X 60' Quadrangle, Idaho And

Geologic Map of the Sandpoint 30´ x 60´ Quadrangle, Idaho and Montana, and the Idaho Part of the Chewelah 30´ x 60´ Quadrangle

Mapped and Compiled by Reed S. Lewis, Russell F. Burmester, Roy M. Breckenridge, Mark D. McFaddan, and William M. Phillips

Idaho Geological Survey Third Floor, Morrill Hall University of Idaho Digital Web Map 189 Moscow, Idaho 83844-3014 2020 Cover photo: View southwest over river delta (Qad) built by the Clark Fork into Lake Pend Oreille. Geologic Map of the Sandpoint 30´ x 60´ Quadrangle, Idaho and Montana, and the Idaho Part of the Chewelah 30´ x 60´ Quadrangle

Mapped and Compiled by Reed S. Lewis, Russell F. Burmester, Roy M. Breckenridge, Mark D. McFaddan, and William M. Phillips 2020

INTRODUCTION

o Geology depicted on this map is based partly on 48 30' 9 2 7 previous 15´ mapping by Harrison and Jobin (1963, 11

1965) and on unpublished 7 ½´ mapping by F. K. Miller 4 and others. Figures 1, 2, and 3 are index maps showing 10 the area covered by our STATEMAP-supported work 2 and mapping by previous workers. Remapping of 11 3 bedrock in 2003-2008 applied some different unit 7 definitions and contact placements for consistency with 1

a n a t n o M recent mapping to the south. We also made additional 2 subdivisions within the Prichard Formation based on a s h i n g t i o n

W 9 6 mapping to the north by Cominco geologists (Michael 8 5 Zientek, written commun., 2003). Overall, the bedrock 9 areas of the eastern part of the map differ little from 48 o Harrison and Jobin (1963, 1965); visual differences are 117 o 116 o attributable to slight changes in placement of contacts 1. Boleneus and others, 2001. and major changes in unit assignment, which affect 2. Doughty, 1995. 3. Etienne, 1988. implied structures. Quaternary deposits were delineated 4. Harrison, 1969. by R.M. Breckenridge during several field seasons 5. Harrison and Jobin, 1963. from the 1980s through 2007. This map replaces a 6. Harrison and Jobin, 1965. preliminary version (Lewis and others, 2008) that 7. Harrison and Schmidt, 1971. 8. Miller, D.M. , unpublished mapping lacked cross sections and unit descriptions. 1980-1993. 9. Miller, F.K., unpublished mapping The most abundant rocks in the Sandpoint area are 1972-1995. low metamorphic grade metasedimentary rocks of 10. Miller, F.K., 2000. 11. Zientek, M.L. and Finch, J.M., the Mesoproterozoic Belt Supergroup (in Canada unpublished compilation, 2003. referred to as the Purcell Supergroup). Most of the high metamorphic grade gneiss and schist of the Priest Figure 1. Primary sources of geologic mapping. Idaho Geological Survey Digital Web Map 189

o 48 30' River complex in the western part of the area appear to

11 12 have protoliths of the same age, consistent with their a n a t n o M derivation from lower strata of the Belt Supergroup. Archean and Paleoproterozoic rocks are present in the

9 10 4 area but probably are tectonic slices of basement rocks. Some igneous rocks date from deposition of the Belt Supergroup, but most granitoids are Cretaceous in age and most hypabyssal rocks are Eocene in age. 7 8 3 2 1

a s h i n g t i o n

W 13 5 6 DESCRIPTION OF ROCK UNITS 48 o 117 o 116 o 1. DWM-24, Burmester and others, 2004c. 2. DWM-25, Burmester and others, 2004a. Intrusive rock classification follows International Union 3. DWM-26, Burmester and others, 2004b. of Geological Sciences nomenclature using normalized 4. DWM-58, Lewis and others, 2006a. values of modal quartz (Q), alkali feldspar (A), and 5. DWM-59, Burmester and others, 2006a. plagioclase (P) on a ternary diagram (Streckeisen, 6. DWM-60, McFaddan and others, 2006. 1976). Mineral modifiers appear in order of increasing 7. DWM-74, Lewis and others, 2006c. 8. DWM-75, Burmester and others, 2006b. abundance for both igneous and metamorphic rocks. 9. DWM-76, Lewis and others, 2006b. Grain size classification of unconsolidated and 10. DWM-88, Lewis and others, 2007c. consolidated sediment use the Wentworth (1922) scale 11. DWM-89, Lewis and others, 2007a. (Lane, 1947). Bedding thicknesses and lamination 12. DWM-90, Lewis and others, 2007b. types are after McKee and Weir (1963) and Winston 13. DWM-91, Burmester and others, 2007. (1986). Grain sizes and bedding thicknesses are Figure 2. Idaho Geological Survey Statemap sources of given in abbreviation of metric units (for example, geologic mapping. dm=decimeter). Unit thicknesses, distances, and

48 o30' elevations are in both metric and English units. 1 Multiple lithologies within a rock unit appear in order of decreasing abundance, and descriptions of stratigraphic

8 4 units are from bottom to top where possible. Soil series are from Weisel and others (1982). Interpretations

5 of kinematic indicators follow Simpson and Schmid (1983) for ductile fabrics, and Petit (1987) and Doblas

a n a t n o M (1998) for brittle ones. Magnetic susceptibilities of hand samples or rock faces measured with a 1995 KT-9 Kappameter from Exploranium G.S. Ltd., appear in 3 a s h i n g t i o n 2 5 Table 1.

W 7

6 48 o 117 o 116 o MAN-MADE DEPOSITS 1. Bennett and others, 1975. 2. Clark, 1967. 3. Green, 1976. m—Historical man-made deposits (Holocene)—Fills 4. Harms, 1982. 5. Harrison and others, 1972. along highways, bridges, railroad right of way, and tres- 6. Hoffer, 2005. tles. Not shown are numerous small fills in and around 7. Miller, 1974. Sandpoint and recent construction along U.S. Highway 8. Miller, 1982. 95. Figure 3. Secondary sources of geologic mapping.

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Table 1. Magnetic susceptibility of intrusive and gneissic rocks in the Sandpoint quadrangle. Values determined from hand specimens or rock faces as measured with a 1995 KT-9 Kappameter from Exploranium G.S. Ltd. and reported in SI units (x 10-3). Magnetite concentration is presumed to be proportional to magnetic susceptibility. Map units ordered the same as in rock descriptions.

Unit Min. Max. Mean n Classification Comments Tl (mt-poor) 0.75 1.8 1.3 2 moderate Tl (mt-rich) 15 19 17 3 high Tum 0.57 4.9 2.7 5 moderate Td 3.3 13 7.6 19 high Tqm (mt-poor) 0.52 1.9 1.3 3 moderate Tqm (mt-rich) 14 25 18 3 high Tggd--Bodie Canyon 6.3 12 9.1 2 high stock Tggd--Wrencoe 2.8 21 12 9 high excluding one diorite sample pluton (0.39) and one fine-grained granite sample (0.07) Kgf 0.02 0.43 0.09 12 low Kmg 0.03 0.89 0.25 16 low excluding 1 mylonitic sample with value of 4.4 Kbg (mt-poor) 0.01 0.48 0.12 32 low Kbg (mt-rich) 1.0 4.7 2.7 6 moderate Kbog 0.02 0.30 0.13 16 low excluding 1 sample with value of 2.9 Khog (mt-poor) 0.03 0.50 0.22 3 low Khog (mt-rich) 14 20 17 3 high Kbgd--Kelso Lake 7.6 27 17 14 high pluton Kbgd--Rapid Lighting 1.7 17 6.0 14 high excluding 1 fine-grained sample Creek pluton with value of 0.09 Kgdf 28 28 28 1 very high Khgd--other plutons 4.6 20 11 7 high Khgd--Salee Creek 0.25 12 4.3 3 moderate pluton Kt 0.35 0.35 0.35 1 low Kgdp--Packsaddle 8.0 13 11 2 high Mtn stock Kgdp--Whisky Rock 2.3 19 12 3 high stock Kqm--Benning Mtn 35 35 35 1 extreme stock KYdi 0.41 0.41 0.41 1 low Ymi 0.06 0.96 0.45 33 low Yam 0.37 0.59 0.45 3 low Yag (mt-poor) 0.09 0.13 0.11 2 low Yag (mt-rich) 13 13 13 1 high Wgn 6.4 7.9 7.2 2 high

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ALLUVIAL, LACUSTRINE, AND Qtl—Talus deposits (Holocene)—Blocky and tabular, poorly sorted angular clasts of Belt Supergroup rocks as MASS-MOVEMENT DEPOSITS talus deposits below cliffs oversteepened by glaciation and flood scour. Locally mined for decorative stone. Qal—Alluvium (Holocene)—Silt, sand, and gravel Mining of these deposits has revealed scour features deposits in modern stream drainages. Moderately- to under the talus aprons. Generally, no soil development. well-sorted silt, sand, and pebble and cobble gravels Shown only in vicinity of State Highway 200 northwest with rare boulders. Mostly reworked glacial deposits in of Cabinet, Idaho. Varied thickness typically 3 to 9 m the lowlands and postglacial colluvium in the mountains. (10 to 30 ft). Typical soils are silt loam to sandy and gravelly loam. Qlm—Lacustrine and fluvial mud deposits (Holo- Soil series of Hoodoo and Wrencoe. Deposits several cene)—Consist of soft clayey silt; locally underlain meters thick. by late glacial outwash, till, or Missoula flood depos- Qaf—Alluvial-fan deposits (Holocene)—Mixed peb- its. Upper limit of the unit along Lake Pend Oreille is ble to cobble gravel deposited as fans at the mouth of controlled by Albeni Falls Dam. The maximum water local drainages. Mostly subangular to angular clasts level is 631.5 m (2,071.7 ft) and the normal minimum derived locally from colluvium and glacial deposits on is 625.1 m (2,051.0 ft). Unit thickens into Lake Pend steep slopes. Soils mainly of the Colburn, Pend Oreille, Oreille basin. Soils include Cape Horn and Hoodoo se- and Bonners series. Thickness 1 to 10 m (3 to 33 ft). ries. Thickness 1 to 10 m (3 to 33 ft).

Qag—Alluvial gravel deposits (Holocene)—Sandy Qbs—Beach deposits (Holocene)—Coarse sand to cobble to boulder gravels in modern flood plains. silty sand and gravel along the shoreline of Lake Pend Rounded and subrounded clasts derived from intrusive Oreille and some of the smaller lakes to the west. Most and Belt Supergroup rocks. Mostly consists of reworked are moderately sorted. Form accreted beaches, bars, and Pleistocene glacial and flood deposits. Soils of the Cape spits in areas of lower wave energy along the shore. Horn and Colburn series. Thickness 5 to 10 m (16 to Deposits lack soil cover. Thickness typically 2 to 5 m 33 ft). (6 to 16 ft).

Qad—Alluvial and deltaic deposits of the Clark Fork Qls—Landslide deposits (Holocene)—Poorly sorted and Pack rivers (Holocene)—Interbedded alluvium and poorly stratified cobble and boulder gravel mixed at the mouth of the Clark Fork and its delta in Lake with sand. Formed by mass movements mainly in till, Pend Oreille (Figure 4). Consists of soft clayey silt; at outwash, and glaciolacustrine sediments and deposited depth is locally underlain by late glacial outwash, till, on glaciated bedrock surfaces. Along shore of Lake or Missoula flood deposits. Thickens into Lake Pend Pend Oreille southeast of Cocolalla, mass movements Oreille to greater than 5 m (16 ft). Soils include Colburn mainly deposited on steep glaciated slopes above Lake and Wrencoe series. Pend Oreille involve bedrock. Under water profiles show extensive landslide and turbidite deposits in the deep lake basin. Soils of the Bonner and Dufort series. Thickness 9 to 30 m (30 to 100 ft).

GLACIAL AND FLOOD-RELATED DEPOSITS

Sediments in the Clark Fork drainage, along valley walls and below the high mountain cirques, date from Pleistocene glaciation when the Cordilleran Ice Sheet repeatedly advanced southward into the quadrangle from Canada. Glacial striations, noted with single-headed Figure 4. View southwest over river delta (Qad) built by the blue arrow on map, exist on both high mountains and in Clark Fork into Lake Pend Oreille. lowlands (Figure 5). Cosmogenic 10Be surface exposure

4 Idaho Geological Survey Digital Web Map 189 ages (mean weighted) constrain the glacial maximum Qgt—Till deposits (Pleistocene)—Dense silt, pebble, ice limit near the Clark Fork ice dam to 14.1 ± 0.6 ka and cobble till with local boulders deposited by the (Breckenridge and Phillips, 2010). Episodic failure of Purcell Trench lobe of the Cordilleran ice sheet. Poorly the ice dam that formed Glacial Lake Missoula caused stratified compact basal till includes ground moraine catastrophic floods, mostly to the south. and some interbedded proglacial deposits. Lateral moraines on the east side of Gold Mountain. Extensive deposits occupy drainages in Rapid Lightning, Grouse, and Sand creeks. Kame terraces along valley margins, specifically along Trestle Creek. Soils include silt loams and gravelly silt loams of the Pend Oreille and Vay- Ardtoo series. Thickness varies; may exceed 50 m (165 ft).

Qgmt—Melt-out till or ice stagnation deposits (Pleistocene)—Varied silty and sandy boulder till and ice contact deposits east of Heath Lake. Unstratified to stratified. Moderately sorted and interbedded with sandy gravels from proximal outwash and meltwater channels. Forms a terminal moraine with hummocky topography from stagnating ice at terminus. Numerous potholes and kettles from melting ice blocks. Thickness varies; may Figure 5. Glacial striations in Mount Shields Formation exceed 10 m (33 ft). (Yms ) west of the mouth of Twin Creek 6.3 km (3.9 mi) 6 — southeast of Clark Fork. Qgm—Deposits of ground moraine (Pleistocene) Silty to sandy boulder till and poorly stratified compact lodgement till include ice contact deposits and some Qglp—Glaciolacustrine and peat deposits (Pleisto- interbedded proglacial deposits. Extensive deposits in cene to Holocene)—Muck, mud, and peat bogs in poor- the Selle lowland north of Lake Pend Oreille and the ly drained paleoglacial outwash channels and kettles of Westmond lowland north of Cocolalla Lake. Includes the lowland north of Lake Pend Oreille. Interbedded kame terraces along the east slopes of the Selkirk with thin layers of fine sand, silt, and clay. Soils of the Mountains west of Sandpoint. Forms drumlin-like Pywell series. Thickness varies from 1 to 5 m (3 to 16 ft). features of molded till between Bottle Bay and Garfield Qgu—Glacial deposits, undivided (Pleistocene)— Bay. Soils include silt loams and gravelly silt loams Mostly loose cobbly silty sand with a silty fine sand of the Pend Oreille and Vay-Ardtoo series. Thickness matrix; pebble- to boulder-sized gravel; includes varies; may exceed 10 m (33 ft). deposits of till and associated proglacial outwash and glacial sediments. Sparse large boulders on bedrock Qgo—Deposits of outwash gravel, undivided and in till. Unstratified to poorly bedded, unsorted to (Pleistocene)—Unsorted to moderately sorted, sandy moderately sorted. In tributary drainages and on slopes pebble to boulder gravel. Rounded to subrounded composed of discontinuous remnants of till and kame granitic and intrusive clasts and subrounded to terraces; on steeper unstable slopes includes mass subangular Belt Supergroup clasts. Coarsely stratified movement deposits. May include some interbedded lake to moderately stratified and locally interbedded with sediments. Soils mainly silt loam of the Pend Oreille ice-contact and proglacial lake rhythmites of silt and series. Thickness ranges from 3 to 30 m (10 to 100 ft). clay. Soils of the Bonner-Kootenai series. Thickness varies; may exceed 50 m (165 ft). Qgta—Alpine till deposits (Pleistocene)—Coarse, blocky, unsorted sandy cobble to boulder till deposited Qgof—Outwash fan deposits (Pleistocene)—Ex- by latest Pleistocene and neoglacial glaciers about tensive deposit of mixed sand, silt and gravel south of 1,500 m (5,000 ft) elevation and higher in the Cabinet Priest Lake forming Jack Pine Flats, probably as co- and Selkirk ranges. These postdate the Late Glacial alescing fans from retreating glaciers. Soil mostly silt Maximum in the Cabinet Mountains. Soils of the Vay- loam and gravely silt loam of the Bonner series. Thick- Ardtoo series. Maximum thickness 15 m (50 ft). ness varies; may exceed 50 m (165 ft).

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Qgg—Outwash gravel deltaic deposits (Pleisto- cene)—Unsorted gravels of poorly rounded pebbles and cobbles; includes proglacial outwash and englacial drift deposits. Those in eastern part of map probably deposited by a post-Missoula floods advance of the Clark Fork ice tongue up the Clark Fork valley into a late Glacial Lake Missoula. Forms large deposit at the mouth of Dry Creek, which exhibits Gilbert-type crossbedding that dips up the Clark Fork valley (Figure 6). Soils of the Pend Oreille series and Vay-Ardtoo association. Thick- ness as much as 15 m (50 ft).

Figure 7. Varves in Glacial Lake Missoula deposit (Qgl), East Fork Lightning Creek. Pen for scale is about 1 cm in diameter.

Qgf—Glaciofluvial deposits (Pleistocene)—Coarse silt, sand, and gravel deposits derived from glacial outwash. Mostly stratified sands and rounded gravels. Oc- cur in channels within and interbedded with Qgl. Near Dover and downstream, unit includes coarse crossbed- ded facies of catastrophic flood gravels from Glacial Lake Missoula floods. Soils are gravelly silt loam to Figure 6. Deltaic deposit (Qgg) formed in Glacial Lake Mis- gravelly sand loam of Bonner-Kootenai series. Thick- soula along the lower end of Dry Creek southeast of Clark ness may exceed 30 m (100 ft). Fork. View to the southwest. Qgoy—Deposits of outwash gravel, young (Pleisto- Qgl—Glaciolacustrine deposits (Pleistocene to Ho- cene)—Unsorted to moderately sorted, sandy pebble locene)—Massive to finely laminated and rhythmites to boulder gravel in the Priest River drainage. Coarsely of clay, silt, and sand deposited in ice-marginal and stratified. Probably formed during the youngest episode postglacial lakes. Unit includes deposits in the Selle, of alpine glaciation in the Selkirk Mountains. Soils of Sagle, and Priest River lowlands and preserved in tribu- the Bonner and Mission series. Thickness 5 to 10 m (16 tary valleys of the Clark Fork as glaciolacustrine silts to 33 ft). with scattered dropstones as deposits of Lake Missoula Qgom—Deposits of outwash gravel, middle (Pleisto- not affected by glacial and flood erosion. Mostly well cene)—Unsorted to moderately sorted, sandy cobble to sorted and finely laminated (Figure 7). Contorted bed- boulder gravel in the Priest River drainage. Coarsely to ding and loading structures are common. Overlain by moderately stratified. Soils of the Bonner series. Thick- glaciofluvial outwash deposits on terraces and in tribu- ness greater than 30 m (100 ft). tary valleys. Soils are silt loam and silty sandy loams of the Mission-Cabinet-Odenson series. Thickness tens of Qgoo—Deposits of outwash gravel, old (Pleisto- meters to over hundreds of meters in drill holes of the cene)—Poorly to moderately sorted, sandy pebble to Selle lowland north of Lake Pend Oreille. boulder gravel above 730 m (2,400 ft) elevation in the Priest River drainage. Soils of the Bonner series. Thick- A measured section more than 50 m (165 ft) thick at the ness 50 m (165 ft), locally greater. junction of Lightning Creek and East Fork Creek was sampled for paleomagnetic study (Breckenridge and Qghcy—Gravel of Hoodoo Channel, young (Pleisto- Othberg, 1998; Meyer, 1999). The measured section is cene)—In south, poorly sorted, coarse boulder outwash capped by a diamicton that may record a late glacial gravels that form the lowest terrace of Hoodoo Channel advance. Soils of the Mission silt loam. and record meltwater flow through Granite Lake to the

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Pend Oreille River. Graded to the outlet of Lake Pend terraces are present upstream from Clark Fork. Locally Oreille at Bayview at an elevation of 670 m (2,200 ft). mantled by silt of the latest phases of Glacial Lake Mis- Contains kettles from melted blocks of ice. Probably soula that postdate episodes of catastrophic flooding. records overflow of Lake Pend Oreille during the last Soils of the Odenson and Wrencoe series. phase of alpine glaciation in the region. Postdates the retreat of Cordilleran ice from the southern end of the Qfgm—Gravel of Missoula floods, middle (Pleisto- Purcell Trench and the last Cordilleran ice dam at Clark cene)—Moderately sorted pebble to boulder gravel. Fork approximately 12,000 years ago. Thickness as Generally, lacks interstitial fines and has clast-sup- much as 18 m (60 ft). ported "boxwork" texture. Moderately stratified to unstratified depending on the depositional landform. Near Qghcm—Gravel of Hoodoo Channel, middle (Pleis- Derr Point, the surface of this unit exhibits giant current tocene)—Poorly sorted very coarse boulder gravels ripples deposited by the latest floods from Glacial Lake with granule and sand matrix that form the middle ter- Missoula about 12,000 years ago. Forms the middle race of Hoodoo Channel and record the lowest elevation of three terraces of flood gravel at about 625 to 645 m of flow through the Spirit Lake portion of the Hoodoo (2,080 to 2,150 ft) in the lower Clark Fork valley. Lo- Channel. Located south-southeast of Hoodoo Lake. cally mantled by silt of the latest phases of Glacial Lake Graded to an elevation of 700 m (2,300 ft). Probably Missoula that postdate episodes of catastrophic flood- resulted from overflow of the Lake Pend Oreille basin ing. Soils of the Odenson and Wrencoe series. during Cordilleran deglaciation of the Purcell Trench or a late ice-marginal and noncatastrophic drainage of Qfgo—Gravel of Missoula floods, old (Pleistocene)— Lake Missoula. Thickness as much as 30 m (100 ft). Moderately sorted pebble to boulder gravel. Generally, Qghco—Gravel of Hoodoo Channel, old (Pleisto- lacks interstitial fines and has clast-supported "boxwork" cene)—Poorly sorted very coarse boulder gravels that texture. Moderately stratified to unstratified depending form the highest terrace of Hoodoo Channel; graded to on the depositional landform. Forms the highest of three approximately 730 m (2,400 ft). Probably records the terraces of flood gravel above 670 m (2,200 ft) in the last emptying cycle of a much diminished and shallow lower Clark Fork valley. Locally mantled by silt of the Lake Missoula. Thickness as much as 30 m (100 ft). latest phases of Glacial Lake Missoula that postdate episodes of catastrophic flooding. Soils of the Odenson Qfg—Gravel of Missoula floods, undivided (Pleisto- and Wrencoe series. cene)—Pebble, cobble and boulder gravel. Includes one or more Qfgb, Qfgy, and Qfgm, described below. Qgsly—Gravel of Spirit Lake, young (Pleistocene)— Poorly sorted bouldery flood gravels deposited as a large Qfgb—Glacial flood bar deposits (Pleistocene)— fan directly from the earlier and larger flood breakouts Crudely sorted and bedded cobble to boulder gravel that from Lake Pend Oreille. Is more extensive to the south form large-scale expansion bars in the lee of bedrock (Lewis and others, 2002). Forms the younger and lower knobs in the Clark Fork valley and downstream along of two high fan surfaces isolated by later flood erosion. the Pend Oreille River. Large-scale crossbeds indicate Soils are cobbly silt loams of the Kootenai series. high-flow regime in deeper water of larger Missoula Thickness as much as 30 m (100 ft). floods. Preserved on the north side of the Clark Fork valley with crests at elevations as high as 850 m (2,800 Qgslo—Gravel of Spirit Lake, old (Pleistocene)— ft). Soils of the Cabinet and Klootch series. Poorly sorted bouldery flood gravels deposited as a Qfgy—Gravel of Missoula floods, young (Pleisto- large fan directly from the earlier and larger flood cene)—Moderately sorted pebble to boulder gravel. breakouts from Lake Pend Oreille. Forms the older and Generally, lacks interstitial fines and has clast-supported higher of two high fan surfaces isolated by later flood "boxwork" texture. Moderately stratified to unstratified erosion. Well exposed immediately south of the map depending on the depositional landform. Surface expres- where surface is marked by giant current ripples with sion of this unit reflects a series of giant current ripples wavelengths of 150 m (500 ft) and amplitudes of 12 m deposited by the latest floods from Glacial Lake Mis- (40 ft). Soils are gravelly silt loam and silt loam of the soula about 12,000 years ago. Forms the lowest of three Kootenai-Rathdrum association mantled by loess and terraces of flood gravel at about 630 to 640 m (2,065 to Mazama volcanic ash (Brownfield and others, 2005). 2,100 ft) in the lower Clark Fork valley. The upper two Thickness greater than 30 m (100 ft).

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COLUMBIA RIVER BASALT deformation that affected the rocks they intruded. Possibly the youngest igneous rocks in the high-grade GROUP Priest River complex, but relationship to Eocene granitic dikes is unknown. Dike east of Elmira Peak contains Tpr—Priest Rapids Member, Wanapum Basalt olivine, actinolite, and chlorite. Moderate magnetite (Miocene)— Medium-gray to dark-gray basalt exposed content (Table 1). near southern map boundary. Typically has a grainy, Td—Dacite dikes and sills (Eocene)—Biotite dacite felty texture caused by abundant small plagioclase and dikes, commonly porphyritic, with blocky phenocrysts olivine phenocrysts and by microvesicles and diktytax- of feldspar as large as 3 cm and biotite phenocrysts itic cavities. Outcrops weather grayish brown to reddish as wide as 5 mm. Most abundant east of Sandpoint brown. The Priest Rapids Member consists of one or but also mapped along the Selkirk Mountains crest. more flows of Rosalia chemical type and has reverse High magnetite content (Table 1). Commonly light magnetic polarity. gray and resistant, forming cliffs and talus slopes. Dikes are 1 to 4 m (3 to 12 ft), rarely 50 m (150 ft) wide. Exposed discontinuously, but some appear to INTRUSIVE ROCKS continue for hundreds of meters. Those concentrated in an approximately 1000 m (3,300 ft) wide swath Tl—Lamprophyre dikes (Eocene)—Biotite lampro- trending north-northwest near the mouth of Pack River phyre dikes with 1 to 2 mm biotite phenocrysts in a termed the Pack River dike swarm by Doughty and fine-grained groundmass (Figure 8). Dikes form two Price (2000). Part of that dike swarm coincides with a groups with moderate or high magnetite content (Table pronounced magnetic anomaly (Kleinkopf and others, 1972), suggesting that at depth there may be a Tertiary 1). One dike that cuts the Sandpoint conglomerate (Tc) pluton formed by amalgamation of such dikes (for northwest of Grouse Creek in the north-central part of example, Glazner and others, 2004). the map yielded a 47.15 ± 0.24 Ma 40Ar/39Ar date on biotite (Doughty and Price, 2000). Generally, deeply Tqm—Quartz monzonite dikes (Eocene)—Fine- weathered and poorly exposed so probably underrepre- grained biotite-hornblende quartz monzonite grades sented on map. to monzonite. Most abundant southeast of Sandpoint. Contain acicular hornblende phenocrysts and lesser amounts of biotite. Dikes form two groups with moderate or high magnetite content (Table 1). Some contain altered pyroxene(?) phenocrysts as long as 4 mm. All contain interstitial potassium feldspar and strongly zoned plagioclase. Notable for low quartz content (<10 percent). Typically altered and possibly related to gold mineralization in the region. Similar to Ta except entirely phaneritic. Unit includes rocks mapped as Cretaceous diabase and diorite and Cretaceous granodiorite by Harrison and Jobin (1965). Single stock of Cretaceous diabase and diorite mapped by Harrison and Jobin (1965) north of Talache was mapped here as three large Tqm dikes based on the mode of occurrence of other rocks of this composition.

Figure 8. Lamprophyre dike (Tl) crosscuts dacite (Td) near Ta—Andesite dikes (Eocene)—Small aphanitic dikes mouth of Pack River. with small hornblende and plagioclase phenocrysts east of Garfield Bay. Possibly related toTqm . Tum—Ultramafic dikes (Eocene)—Fine- to coarse- grained pyroxene(?)-olivine(?) rocks, now largely Tggd—Granite and granodiorite (Eocene)—Medi- altered. Occurs as dikes along the Selkirk Mountains um-grained, porphyritic, hornblende-biotite granodio- crest as well as in Ypmt east of Elmira Peak. Absence of rite, fine- to medium-grained, equigranular, biotite gran- visible fabric in the dikes suggests they postdate ductile ite, and minor biotite-hornblende diorite. Includes the

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Wrencoe pluton in the western part of map and associat- PRIEST RIVER COMPLEX ed outlying stocks. Granodiorite and granite intimately INTRUSIVE SUITE mixed in the northern part of the pluton and present together at several outcrops. Biotite granite contains anhedral, interstitial potassium feldspar and strongly zoned Plutons emplaced in metamorphosed rocks of the Belt plagioclase feldspar. Dark quartz at some localities may Supergroup. indicate a relatively high U content. High magnetite content (Table 1). Granodiorite contains hornblende in Kgf—Fine-grained granite and granodiorite (Cre- addition to biotite, potassium feldspar phenocrysts 1 to 5 taceous)—Fine- to medium-grained biotite and mus- cm in length, and a high magnetite content. Tggd locally covite-biotite granodiorite and granite exposed in the contains small diorite bodies as well as mafic inclusions northern part of the map. Locally foliated or lineated. with textures indicating the mafic magmas mixed with Both muscovite-biotite and biotite-only phases contain the porphyritic felsic magmas (Figure 9). Sample col- moderately to strongly zoned, subhedral to euhedral lected near Wrencoe was dated at 50.1 ± 6.3 Ma (U-Pb plagioclase, which is suggestive of relatively rapid cool- zircon; Whitehouse and others, 1992). Another sample ing. Low magnetite content (Table 1). Also present as was dated by U-Pb zircon methods (CA-TIMS) at about small unmapped bodies within other units. Zircons from 47.9 Ma (Stevens and others, 2016). Termed the “grano- east of Pack River near Tavern Creek yielded a U-Pb diorite of Wrencoe” (Miller and others, 1999). Also in- age of 71.7 ± 1.8 Ma (laser-ablation inductively coupled cludes the monzogranite porphyry of Bodie Canyon mass spectrometry methods; Richard Gaschnig, written north of Priest River to which Miller and others (1999) commun., 2012). assigned a Cretaceous age. Chemical similarity (high Sr content) of this body to the main Wrencoe pluton is Kpeg—Pegmatite and fine-grained biotite granodio- the justification for our Eocene age assignment for the rite (Cretaceous)—Coarse-grained muscovite-biotite Bodie Canyon body. pegmatite and leucocratic fine- and medium-grained aplite and alaskite. Fabric generally distinct but appears to share parting or jointing with rocks it intrudes, perhaps because form is sill-like along foliation. Constitutes mappable masses locally, for example, south of Caribou Creek, but more commonly comprises 5 to 30 percent of all metamorphic and igneous rocks in the Priest River complex.

Kmg—Biotite-muscovite granite and granodiorite (Cretaceous)—Massive to foliated and lineated biotite-muscovite and muscovite-biotite granite and granodiorite. Unit includes abundant pegmatite, mixed granitic rocks west of Sand Creek, and granitic rocks of Algoma Lake (Miller and others, 1999) in the northern Figure 9. Concentration of mafic enclaves in porphyritic and central part of the map. Plagioclase is weakly phase of Wrencoe Pluton (Tggd). zoned; myrmekite is common. Muscovite 7 to 15 Tdg—Diorite and gabbro (Eocene)—Mafic rocks percent; biotite 3 to 8 percent. Low magnetite content exposed near the southeast part of the Wrencoe pluton. (Table 1). Foliation only formed locally; where present, Hornblende, pyroxene(?), and plagioclase are the is typically mylonitic. Kinematic indicators such as S-C primary constituents. Presumed to be a mafic phase fabrics and sheared porphyroblasts indicate top-to-the- of the pluton, which contains mafic inclusions and east motion. Age uncertain. unmapped mafic phases. Kmgp—Porphyritic biotite-muscovite granite and TKfd—Felsic dikes (Eocene or Cretaceous)—Fine- granodiorite (Cretaceous)—Exposed west of Cocolalla grained biotite- or biotite-hornblende-bearing felsic Lake where it was mapped as monzogranite of Long dikes. Rocks locally exhibit extreme L-S fabrics Mountain by Miller and others (1999) and described attributed to intrusion during regional extension. Fine as biotite-muscovite monzogranite distinguished by grain size suggests intrusion into cool rock and therefore muscovite megacrysts averaging 2 cm across. Pegmatite relatively young age. and aplite dikes abundant. Varied mylonitic fabric,

9 Idaho Geological Survey Digital Web Map 189 with both west- and east-dipping mylonitic foliations Kbog—Biotite granite and granodiorite gneiss (Cre- showing tops-to-the-east kinematics. See Hoffer (2005) taceous)—Foliated, medium-grained biotite orthog- for whole-rock geochemical data and fission-track study neiss in western part of map. Includes granite, granodi- of this unit. orite, and tonalite. Locally contains minor hornblende. Includes the mixed leucocratic granitic rocks of Lost Kbg—Biotite granodiorite and granite (Creta- Creek mapped by Miller and others (1999) who noted ceous)—Massive to foliated and lineated biotite grano- extreme textural and compositional variation. Locally diorite and granite (Figure 10). Includes mixed granitic contains primary muscovite and is typically mylonitic. rocks of Camels Prairie, granodiorite of Falls Creek, Magnetite content typically low but locally moderate in granitic rocks of Jewel Lake, and granodiorite of Saw- mylonitic rocks (Table 1). yer as mapped by Miller and others (1999). Locally contains lenses of metasedimentary rock similar to what is Khog—Hornblende-biotite granodiorite and tonal- mapped separately as Ygs. Includes both medium- and ite gneiss (Cretaceous)—Foliated, medium-grained fine-grained phases; the latter is subordinate and may be hornblende-biotite orthogneiss, with locally conspicu- related to Kgf. Biotite 5 to 19 percent; minor amounts ous feldspar megacrysts and lenticular quartz grains. of fine-grained (secondary?) muscovite present locally. Tonalite and granodiorite sills, typically mylonitic, Plagioclase is weakly zoned; myrmekite is common. in the western part of map. Locally lacks hornblende. Magnetite content typically low but locally moderate in Magnetite content low or high (Table 1). Probably simi- some mylonitic rocks and in rocks near Eocene plutons lar in age to the Newman Lake gneiss, a large body of (Table 1). Mylonitic foliation is similar to that found in orthogneiss exposed along the western side of the Spo- Kmg. kane dome (Weis, 1968; Weisenborn and Weis, 1976).

HIGH-LEVEL INTRUSIVE SUITE

Plutons with narrow contact aureoles in Belt Supergroup rocks. Kpd—Porphyritic dacite (Cretaceous)—Hornblende- biotite dacite with feldspar phenocrysts. Includes sills in northeast part of map and exposure east of Clark Fork between Antelope and Sugarloaf mountains in veined, magnetite-rich, “dike fault” of Harrison and Jobin (1963) where it was dated as 89.8 ± 0.1 Ma (total 40Ar/39Ar gas age; Fillipone, 1993). Kbgd—Biotite granodiorite (Cretaceous)—Medium- to coarse-grained biotite granodiorite and granite exposed in the central and northwestern parts of map. Minor amounts of biotite-hornblende quartz diorite are also present. Includes the granodiorite of Kelso Lake, granodiorite of Rapid Lightning Creek, and Galena Point Granodiorite described by Miller and others (1999). Variably porphyritic with commonly zoned and Carlsbad twinned K-feldspar phenocrysts 1 to 4 cm long. Quartz typically 2 to 5 mm anhedral grains or assemblages of grains (Figure 11). Feldspars subhedral. Biotite in subhedral to euhedral books 2 to 5 mm thick constitute Figure 10. Biotite granite (Kbg) along the road to Schweitzer 5 to 10 percent of the rock. Abundant epidote and Basin. titanite. Northwestern exposures include granodiorite of Dubius Creek and monzogranite of Big Meadows that Miller and others (1999) described as muscovite-

10 Idaho Geological Survey Digital Web Map 189 biotite monzogranite and granodiorite. Assignment here Khgd—Hornblende-biotite granodiorite (Creta- to Kbgd based on absence or paucity of muscovite at ceous)—Medium-grained hornblende-biotite granodio- most localities and the uncertainty of contact placement. rite. Includes the granodiorite of Salee Creek, the grano- Most abundant muscovite is southwest of Dubius Creek. diorite of Lightning Creek, and the northern part of the Kelso Lake and Rapid Lightning Creek plutons have granodiorite of Whiskey Rock described by Miller and high magnetite content with Rapid Lightning Creek others (1999). Unfoliated to well foliated. Lightning pluton being somewhat lower (Table 1). Unit generally Creek stock has approximately 500 m wide contact au- weathers to form low topography but southern part of reole with andalusite (Fillipone and Yin, 1994). High Rapid Lightning Creek pluton near Tertiary dike swarm magnetite content in most plutons but moderate in parts is more resistant. U-Pb ages for Kelso Lake pluton are of Salee Creek pluton and small bodies east of Elmira 88 ± 9 Ma for zircon and 88 ± 0.5 Ma for titanite (Joe L. (Table 1). Salee Creek pluton consists of medium- to Wooden, written commun., 1994, in Miller and others, coarse-grained biotite-hornblende granodiorite contain- 1999). K-Ar age of 80.7 ± 2 Ma obtained for biotite ing about 15 to 20 percent mafic minerals. Plagioclase, from pluton east of Purcell Trench fault dates cooling quartz, and potassium feldspar are anhedral; hornblende below about 300°C. Muscovite and biotite from body is euhedral in prismatic crystals as large as 4 to 12 mm; southwest of Priest Lake gave potassium-argon ages of biotite forms hexagonal books 4 to 5 mm wide. Potas- 102 and 95 Ma, respectively (Miller and Engels, 1975, sium feldspar is also interstitial. Titanite, epidote, and recalculated using current IUGS constants). Zircons allanite are accessory minerals. Lightning Creek stock from Kbgd along Gold Creek near the Boise Meridian in consists of medium-grained hornblende-biotite grano- the southwest part of the Rapid Lightning Creek pluton diorite containing about 8 to 15 percent mafic minerals. yielded a U-Pb age of 107.4 ± 1.0 Ma (laser-ablation Titanite and epidote are accessory minerals. A U-Pb zir- inductively coupled mass spectrometry methods, con age of 94 ± 5 Ma was obtained from the Salee Creek Richard Gaschnig, written commun., 2012). See Hoffer pluton (Joe L. Wooden, written commun., 1994, in Mill- (2005) for whole-rock geochemical data and fission- er and others, 1999). An 40Ar/39Ar weighted mean age on track study of the Kelso Lake pluton. hornblende of 99.55 ± 0.16 Ma (steps 9 to 13, 87.8 percent gas; Fillipone and Yin, 1994) does not support pro- tracted cooling. Lightning Creek stock ages from biotite of 71.7 Ma (K/Ar; recalculated from Miller and Engels, 1975) and 71.4 ± 0.7 Ma (40Ar/39Ar plateau age; Filli- pone and Yin, 1994) date cooling below biotite closure temperature during uplift. Age on hornblende of 75.7 ± 0.3 Ma from 40Ar/39Ar integrated over last 85.1 percent gas released (Fillipone and Yin, 1994) is likely closer to emplacement age. Emplacement pressure was 4.6-5.5 kb (about 12-15 km depth) calculated from aluminum in hornblende (Fillipone and Yin, 1994). Zircons from the southern pluton near Granite Point yielded a U-Pb age of 88.6 ± 1.0 Ma (laser-ablation inductively coupled mass spectrometry methods, Richard Gaschnig, written commun., 2012) indicating that plutons of this unit have Figure 11. Biotite granodiorite (Kbgd) near North Callahan diverse ages. Creek northeast of Calder Mountain. Kgdf—Fine-grained granodiorite (Cretaceous)— Kt—Hornblende-biotite tonalite (Cretaceous)— Hornblende-biotite granodiorite exposed only along the Mapped as tonalite of Clagstone in southwest part of eastern edge of the Kelso Lake pluton near the southern map by Miller and others (1999), who described unit map boundary. Fine grained but contains medium- to as highly mafic, coarse-grained, moderately to weakly coarse-grained parts typical of Kbgd. Hornblende foliate biotite-hornblende tonalite. Contains abundant abundant to rare; titanite and epidote abundant and titanite and epidote. Low magnetite content (Table 1). conspicuous. Very high magnetite content (Table 1). Compositionally gradational into Khgd to the east, but Could be a chilled margin of the Kelso Lake pluton apparently about 6 m.y. older. Titanite yielded U-Pb age against the Salee Creek pluton (Khgd). of 94.0 ± 0.5 Ma (Joe L. Wooden, written commun. in

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Miller and others, 1999). Hornblende yielded a 78.26 ± KYdi—Diorite dike (Mesoproterozoic to Creta- 0.12 Ma 40Ar/39Ar integrated age over 50.6 percent gas ceous)—Single hornblende diorite dike west of Goat released (David Miller, written commun., 2003). Creek near east edge of map. Mafic content (hornblende and actinolite) about 40 percent. Low magnetite content Kgdp—Granodiorite porphyry (Cretaceous)— (Table 1). Age highly uncertain, but likely Mesoprotero- Hornblende-biotite granodiorite porphyry in south-cen- zoic or Cretaceous. tral part of map. Includes the southern part of the granodiorite of Whiskey Rock and granodiorite porphyry of Packsaddle Mountain described by Miller and others OLDER DIKES AND SILLS (1999). Blocky phenocrysts of plagioclase as long as 1 cm, and biotite and less hornblende as long as 4 mm in Moyie Sills—Mafic to quartz-bearing intrusions in the gray groundmass of feldspar, quartz, and biotite. High Prichard Formation. Similar to the sills described by magnetite content in Packsaddle Mountain and Whis- Bishop (1976) from about 50 km (30 mi) north. Most key Rock stocks (Table 1). Both bodies have roofs of are quartz tholeiites or differentiates from tholeiitic _l; body on Packsaddle Mountain also has a floor of magma intruded into the Prichard Formation. Sills _l. Intrusion is interpreted as a single laccolith that has lower and higher in the Aldridge Formation (Prichard been fault offset during eastward tilting (Burmester and correlative in Canada) appear to be distinct chemically, Lewis, 2011). Zircons from near Whiskey Rock yielded with the higher set having a higher Ti/Zr trend than a U-Pb age of 100.1 ± 1.3 Ma (laser-ablation inductive- the lower ones (Anderson and Goodfellow, 2000), and ly coupled mass spectrometry methods, Richard Gasch- seem to have intruded in at least two separate events. nig, written commun., 2012). A more recent regional geochemical study (Rogers and others, 2016) also found at least two distinct Kgdm—Megacrystic biotite granodiorite (Creta- geochemical groups. Early intrusions were at shallow ceous)—Medium-grained porphyritic biotite grano- levels during or closely following sedimentation of the diorite. Only present east of Priest Lake at the northern Lower Aldridge equivalent Ypab (Höy and others, 2000; map boundary where it was termed mafic granodiorite Gorton and others, 2000; Cressman, 1989; Sears and of Cavanaugh Bay (Miller and Burmester, 2004). Potas- others, 1998; Poage and others, 2000). Generation of sium feldspar megacrysts 15 mm to 4 cm in length form Ypm was probably synchronous with this activity. Later augen where unit is foliated. intrusions have chilled margins and contact aureoles, evidence that they invaded consolidated rock. Age of Kqm—Biotite-hornblende quartz monzonite (Cre- most sills in and near Ypab is probably close to U-Pb taceous)—Biotite-hornblende quartz monzonite. Ex- dates on zircons near Kimberley, British Columbia posed in a single medium-grained pluton in the north- about 160 km (100 mi) north-northeast of Sandpoint east part of map on the east side of Benning Mountain (1,468 ± 2.5 Ma; Anderson and Davis, 1995) and from stock. Etienne (1987, 1988) reported lath-shaped feld- southeast of Plains, Montana, about 180 km (110 mi) spar phenocrysts set in an equigranular groundmass and southeast (1,469 ± 2.5 Ma; Sears and others, 1998). a mode of 40 percent plagioclase, 35 percent potassium Age of the younger sills may be that of the Paradise sill feldspar, 7 percent amphibole, and 5.5 percent quartz. near the base of the Prichard Formation there (1,457 ± The remainder is epidote, titanite, sericite, allanite, 2 Ma; Sears and others, 1998). One sill in Ypab in the apatite, zircon, ilmenite, magnetite, pyrite, and hema- hanging wall of the East Newport fault south of Benton tite. The one sample we collected contained strongly Creek has chemical affinity to the Plains sill (Chris zoned plagioclase, about 2 percent biotite, 10 percent Rogers, written commun., 2014) so probably belongs hornblende, and abundant magnetite but was otherwise to the older sill set. Another near the confluence of similar mineralogically to the sample reported by Eti- Trout Creek and Pack River has affinity with sills near enne (1987). Extreme magnetite content (Table 1). Zir- the lower-middle Aldridge contact in Canada (Chris Rogers, written commun., 2014), also consistent with cons from near Benning Mountain yielded a U-Pb age intrusion into Ypab. of 110.6 ± 1.2 Ma (laser-ablation inductively coupled mass spectrometry methods, Richard Gaschnig, written Ydb—Diabase sill (Mesoproterozoic)—Fine-grained commun., 2012). hornblende plagioclase mafic intrusion. Occurs as

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thin sill low in Yb on Scotchman Peak (Figure 12) interlayered with coarser phases within the body parallel and at same stratigraphic level southwest of the Hope to upper and lower conformable contacts. Characterized fault. Rock is jade green and, although altered or by higher concentration of quartz-rich differentiates, greenschist metamorphosed (chlorite+epidote+calcite), commonly toward the top, than typical Ymi. Granophyre it contains relict hornblende. Age of tuff near top of blotches as large as 2 cm across common. Hornblendite Wallace Formation in Glacier National Park (Winston, has acicular amphibole 2 cm long in contrast to common 2007) of 1,454 ± 9 Ma (Evans and others, 2000) is stubby form. Sill varies in thickness and composition indistinguishable from the 1,457 ± 2 Ma age (Sears and along strike; local variants are mapped separately as Yqd others, 1998) of the Paradise sill low in the Prichard and Ygb. Identified as the middle or “C” sill of Bishop Formation near Plains, Montana, about 130 km (80 mi) (1973, 1976) based on occurrence low in Ype. southeast of Scotchman peak so Ydb likely is a young Moyie sill. Ygg—Granophyric granite (Mesoproterozoic?)— Fine-grained granophyric granite. Found as sill low in Ypt on top of Goat Mountain and at same stratigraphic level southeast and west to northwest of Scotchman Peak. Assigned a Cretaceous age by Harrison and Jo- bin (1963) but granophyric and concordant nature more similar to Proterozoic sills elsewhere.

Yam—Amphibolite (Mesoproterozoic)—Foliated to massive amphibolite sill-like bodies in the Priest River complex. Garnetiferous near Colburn and east of Elmira (Figure 13) where they record peak metamorphic conditions of about 6 kb and 720°C (Doughty and Price, 2000). Zircon ages of 1,470-1,430 Ma (Doughty and Chamberlain, 2008) are consistent with them being Figure 12. Diabase sill (Ydb) exposed on west ridge of metamorphic equivalents of mafic sills in the Prichard Scotchman Peak low in the Burke Formation. Formation. Small bodies within Ygs nearby and west of the Pack River may have same origin. Low magnetite Ymi—Mafic intrusive rocks, undivided content in single sample measured (Table 1). (Mesoproterozoic)—May include one or more of the varieties described below (Yqd or Ygb). Low magnetite content (Table 1).

Yqd—Quartz diorite (Mesoproterozoic)—Medium- grained biotite quartz diorite and biotite-hornblende quartz diorite. Occurs as middle and upper parts of apparently differentiated mafic sills and as separate sills. Exhibits some granophyric intergrowth. Best exposures of the differentiated sills occur northeast of Hope along the Strong Creek-Round Top mountain trail and near the summit of Round Top Mountain.

Ygb—Gabbro (Mesoproterozoic)—Medium-grained hornblende gabbro. Generally, quartz bearing. Appears to grade upward over short distance to Yqd with increasing quartz and decreasing hornblende. Figure 13. Garnet porphyroblasts in amphibolite (Yam), now Ymic—Crossport C mafic sill (Mesoproterozoic)— with biotite instead of amphibole, west of Elmira. Fine- to coarse-grained hornblende gabbro, quartz diorite, and hornblendite. Finer grained varieties are typically near bottom and top of sill, but they also occur

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CENOZOIC STRATA Near intrusive contacts, the limestone is coarsely crystalline white marble. Bush (1989) described six lithofacies (lime mudstone, nodular shale, mottled Tc—Sandpoint conglomerate (Eocene)—Moderately lime mudstone, dolopackstone, dolobindstone, and to poorly sorted conglomerate containing angular to dolomudstone) near Lakeview, immediately south of subrounded clasts of Mesoproterozoic mafic sills (Ymi), the map boundary. The lower part of the unit contains laminated siltite and argillite, siltite, and quartzite of several genera of trilobites and brachiopods and is the Prichard Formation, and rare clasts of hypabyssal Middle Cambrian (Harrison and Jobin, 1965; Bush, intrusive rocks. Mafic sill clasts as large as 10 m, other 1989). Unit west of lake consists of light gray to white lithologies typically 2 to 20 cm (Figure 14). Grain weathering recrystallized limestone exposed in a down- size decreases southwest where bedding is better faulted block east of the Salee Creek pluton. Contains defined by green silt and fine sand. No clasts of high minor, varied fine to medium siliciclastic grains and metamorphic grade or plutonic origin were observed. traces of sub-millimeter magnetite grains. The thin Matrix has abundant chlorite and epidote. Eocene age (30 m? 90 ft?), nonresistant Rennie Shale presumably 40 39 is based on 51.5 ± 0.5 Ma and 49.7 ± 0.3 Ma Ar/ Ar underlies the Lakeview Limestone in this area, but the biotite plateau ages of dike or volcanic clasts from the contact was not observed. Estimated to be at least 610 m conglomerate exposures east of Colburn and a 47.15 ± (2,000 ft) thick east of Lake Pend Oreille on Packsaddle 0.24 biotite plateau age of a lamprophyre dike that cuts Mountain (Harrison and Jobin, 1965). Bush (1989) the conglomerate (Doughty and Price, 2000). reported 637 m (2,090 ft) to the south near Lakeview.

_r—Rennie Shale (Cambrian)—Fossiliferous, olive to brown, papery fissile shale mapped by Harrison and Jobin (1965) west of Packsaddle Mountain near the southern map boundary. Unit contains trilobites and brachiopods and is Middle Cambrian (Harrison and Jobin, 1965). Poorly exposed and included with underlying Gold Creek Quartzite (_gcr) except in three localities on the map.

_gcr—Gold Creek Quartzite and Rennie Shale, undivided (Cambrian)—Quartzite and conglomerate exposed east and west of Lake Pend Oreille near the southern map boundary. East of the lake, Harrison and Jobin (1965) reported a basal conglomerate a few feet thick containing a few cobbles of Belt rocks but principally quartz pebbles in a matrix of poorly sorted sand. Above that is slightly feldspathic, pink to buff or white fine- to coarse-grained quartzite Figure 14. Sandpoint conglomerate (Tc) exposed in quarry near Colburn. Clasts are mostly Mesoproterozoic (Prichard containing scattered pebbles and pebble beds. The basal Formation and Moyie sills) derived from the east. conglomerate contains a few cobbles of Belt Supergroup rocks but consists principally of quartz pebbles in poorly sorted sand. Harrison and Jobin also reported PALEOZOIC STRATA jasper with no known local source. West of Lake Pend Oreille consists of medium- to thick- bedded quartzite; _l—Lakeview Limestone (Cambrian)—Fossiliferous some is thinly banded, but all banding may not represent limestone exposed east and west of Lake Pend Oreille sedimentary layering. Typically, white and medium to near the southern map boundary. East of the lake, coarse grained, but commonly stained yellow or orange; Harrison and Jobin (1965) reported light- to dark-gray locally conglomeratic and poorly sorted. Much of unit or black, thin-bedded, blocky to massive limestone in is semi-friable, apparently due to chemical alteration. the lower part and dolomite in the upper part. Most of Metamorphosed near plutonic rocks to coarse quartzite the rock is recrystallized in patches and irregular streaks. with accessory muscovite and magnetite. Estimated to

14 Idaho Geological Survey Digital Web Map 189 be 120 m (400 ft) thick east of Lake Pend Oreille on Kidder's (1987) subdivisions would be easier to main- Packsaddle Mountain (Harrison and Jobin, 1965). tain where the rocks are metamorphosed. Best exposed on Antelope Mountain east of Clark Fork and near Bea- ver Peak in the southeast corner of the map. BELT SUPERGROUP

Yl3—Libby Formation, member 3 (Mesoprotero- This lithostratigraphic unit spans the international zoic)—Microlaminated to laminated, dark-gray to black boundary but carries different group, formation, and argillite and light-gray to white siltite interstratified with member names on either side of the border. Of the laminated pale-green argillite and olive siltite, scattered units south of the Canadian border, the stratigraphically carbonate layers of low domal stromatolites, and thin highest is the Missoula Group, which includes all Belt (less than 10 cm) oolite beds. Mudcracked tops, mud units above the Piegan Group (Figure 15). It is similar to chips, and small-scale cross-laminated bases common the Ravalli Group below the Piegan Group in that it is a within the green siltite and argillite intervals. Olive siltite clastic wedge (quartzite, siltite, and argillite) but had a commonly dolomitic and weathers to characteristic different source (Ross and Villeneuve, 2003). The lowest tan color. Silicification varied, but especially common unit, which constitutes about half the total thickness within pale-green argillite and argillite mud chips of the Belt Supergroup, but lacks group status, is the (Figure 16). Exposed in cliffs north of Clark Fork River; Prichard Formation. Previous mapping in this region poorly exposed on ridges south of the river. Similar to did not subdivide the Prichard Formation (Harrison and Kidder's (1987) member C except that Yl3 includes Schmidt, 1971) or subdivided only the top (Cressman some carbonate near the base. Top eroded, but thickness and Harrison, 1986). Here, we apply alphabetic member to the east approximately 370 m (1,210 ft). Harrison and assignments that Cressman (1989) used south of 48 Jobin (1963) reported a thickness of 300 m (1,000 ft) degrees north latitude (Figure 15). Assigning quartzite for their argillite, siltite, and dolomite member south of packages with similar characteristics to different Clark Fork, Idaho. members was facilitated by release of mapping by Cominco with control based on “markers” (Michael Yl2—Libby Formation, member 2 (Mesoproterozo- Zientek, written commun., 2003). These markers served ic)—Laminated to less commonly microlaminated pale- for the upper units down through Ype. Our attempt to green to olive siltite and lighter green argillite. Siltite identify lower units is based on patterns of alternating layers, commonly a few centimeters thick with much fine/thin versus coarse/thick sequences matched to thinner argillite caps, commonly display loaded bases the subdivisions of Finch and Baldwin (1984) in and and internal low-angle cross-lamination. Silt-filled near the area, and Cressman (1985) from near Plains, cracks as deep as 5 cm disrupt both siltite and argillite Montana, about 100 km (60 mi) to the southeast. See layers; most are probably mudcracks but some may be Harrison and Jobin (1963) for the history of naming dewatering structures. Thin mud chips of pale-green Belt Supergroup units in the area; reasons for departures argillite ubiquitous and commonly silicified. Silicifica- from their naming scheme are explained below within tion of strata most common within the millimeter-thick descriptions of affected units. argillite layers. Silicification of both siltite and argillite is patchy throughout unit, rarely as apparently silicified argillite masses filling voids as if injected as fluid be- MISSOULA GROUP tween bedding planes, inflating the strata. Upper part of unit contains multiple layers of low, domal stromatolites Libby Formation (Mesoproterozoic)—Laminated to and punky, recessively weathering layers of oolite 1 to microlaminated dark-gray to black argillite and white 10 cm thick. Upper contact placed above concentrated to light-gray to pale-green siltite, tan-weathering dolo- stromatolitic and oolitic carbonate beds and below a mitic siltite, oolite, and stromatolites. Highly resistant, concentration of microlaminated to laminated white chert-like material superficially resembling argillite siltite and black argillite at base of Yl3. Best exposed on commonly occurs as silicified mudcracked tops of silt- cliffs northwest of Cabinet. Unit is similar to Kidder's ite and argillite couplets and mud chips. We followed (1987) member B but excludes gray argillite at base and Harrison and Jobin’s (1963) subdivisions of the Libby top that he included in B. Thickness about 180 m (590 Formation because the same system was used to the east ft); corresponds to calcareous member of Harrison and in Montana (Harrison and others, 1992), even though Jobin (1963).

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Quaternary Qg glacial deposits Miocene Tcr Columbia River Basalt Group Northern Idaho Cambrian OCs Lakeview Limestone Gold Creek Quartzite and Rennie Shale Libby Formation Ymiu Bonner Formation

Mt. Shields Formation Missoula Group Shepard Formation Ymil Snowslip Formation

Ypi Wallace Formation Piegan Group Location of stratigraphic column Western facies of Helena Formation St. Regis Formation Revett Formation Yra Ravalli Group Burke Formation Rock type

transition member limestone

member h dolomitic siltite member g quartzite

member f siltite

argillite member e Yp gneiss and member d Mesoproterozoic schist member c Prichard Formation orthogneiss Belt Supergroup and related rocks mafic sill members a and b basalt flows

gravel

3 km

Hauser Lake gneiss and related rocks 1 Ygs

Metamorphosed 0 Prichard Formation

Yagl

Laclede augen gneiss

Paleoproterozoic Gold Cup Quartzite XAm and Archean Pend Orielle gneiss ~ 2650 Ma basement

Figure 15. Composite stratigraphic column for Belt Supergroup and related rocks in northern Idaho. Qg-glacial deposits, Tcr-Columbia River Basalt Group, O_s-sedimentary rocks, Ymiu-upper Missoula Group, Ymil-lower Missoula Group, Ypi-Piegan Group, Yra-Ravalli Group, Yp-Prichard Formation, Ygs-gneiss, schist, and quartzite, Yagl-Laclede augen gneiss, XAm-metamorphic rocks (Lewis and others, 2012).

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nal lamination of quartzite beds commonly defined by discontinuous wisps of red argillite or thin red argillite mud chips. Some parting surfaces nearly covered with detrital muscovite flakes as wide as 4 mm across. Base is gradual transition from the underlying dark-green

and gray laminated siltite and argillite of Yms6 with increasing abundance of 10 to 30 cm tabular light- to medium-green quartzite beds. These have thin, discontinuous lenses or lags of well-rounded medium quartz grains, less feldspar than overlying red quartzite, and typically millimeter-thick, cracked light-green argillite caps. Some green siltite with millimeter-thick black laminated caps also present. Higher in the section, well- Figure 16. Silicified mud chips in member 3 of the Libby Formation (Yl ) near the summit of Antelope Mountain. rounded medium quartz grains occur in wispy lenses of 3 white sand lags typically less than 1 cm thick at bases of some red quartzite beds. Interstratified with the red Yl1—Libby Formation, member 1 (Mesoproterozo- ic)—Laminated to microlaminated light-gray to white quartzite are intervals of laminated pink quartzite and to green siltite and dark-gray to black argillite and mi- red argillite as well as wavy-laminated green siltite and nor dolomitic gray siltite and stromatolites. Lamina- green argillite in zones 10 to 30 cm thick. These zones tion mostly wavy and uneven. Graded gray siltite and decrease upwards from constituting about half to about black argillite couplets locally disrupted by ptygmatic one quarter of the strata. At the top of Ybo are minor silt-filled cracks. Elsewhere, lamination thinner with very thin beds of green quartzite, overlain by several more distinct siltite and argillite laminae. Commonly beds of white quartzite 5 to 10 cm thick with well- rusty weathering. Includes scattered and discontinu- rounded medium quartz grains. Upper white quartzite is ous gray siltite layers as thick as 5 cm, with olive cen- less feldspathic than lower pink quartzite. Upper contact timeter-scale siltite beds more abundant in upper part placed at lowest appearance of dark-gray argillite and and low domal stromatolites at the top. Upper contact gray to white siltite of overlying Yl1. Zircons from a thin is placed above the stromatolitic zone that is above the tuff at this contact about 40 km (25 mi) to the northeast highest occurrence of the microlaminated white siltite yielded an age of 1,401 ± 6 Ma (U-Pb; Evans and oth- and black argillite. Distinguished from other black ar- ers, 2000). Three or more distinct marker horizons that gillite units by white and black striped appearance and may be other tuffs are present within the Bonner For- ptygmatic siltite dikelets, as well as thin zones of locally mation. The markers consist of 5 to 20 cm of couplets contorted and folded microlaminations and laminations to couples of dark-purple to nearly black, flat-laminated within parallel-laminated intervals. Unit is best exposed siltite and thinner light-green argillite. The marker ho- in roadside cliffs along State Highway 200 north of rizons are distinctly smooth and fracture conchoidally; Cabinet; also exposed above Antelope Lake. Similar to the lowest two occur approximately 61 m (200 ft) from Kidder's (1987) member A but includes about 10 m (30 the base of the unit where predominately green quartz- ft) of carbonate-bearing (stromatolitic) layers included ite passes upward into predominately red quartzite. The in Kidder's member B. Thickness about 75 m (250 ft); next marker is approximately 61 to 91 m (200 to 300 ft) corresponds to laminated argillite and siltite member of higher in the section within predominately red quartzite. Harrison and Jobin (1963). Unit distinguished from Yms1-3 by medium sand grains Ybo—Bonner Formation (Mesoproterozoic)—Pink, in basal lags, coarser and generally more abundant mus- red, and green fine- to medium-grained feldspathic covite on some parting surfaces, wispy occurrence of quartzite, siltite, and argillite typically exposed in re- argillite and thin chips in decimeter-thick quartzite beds, sistant cliff outcrops in the area (Figure 17). Character- less common ripples and mudcracks, lack of salt casts, ized by tabular beds 10 to 30 cm thick of flat-laminated and greater abundance of rusty spots in many quartz- pink quartzite with microlaminated to laminated red ite beds. Unit is most continuously exposed northwest argillite caps. Contains less potassium feldspar than of the Twin Creek fault along USFS Road 332 (High plagioclase; some plagioclase may be secondary, but Road), and less continuously but well-exposed above potassium feldspar content is low, nevertheless. Inter- Antelope Lake. Thickness is approximately 275 m (900

17 Idaho Geological Survey Digital Web Map 189 ft) and thus greater than the 200 to 210 m (650 to 700 ft) with horizontally microlaminated to laminated and estimated by Harrison and Jobin (1963). Equivalent to cross-laminated siltite and argillite (Figure 18); some Bonner Quartzite in the Missoula area (Nelson and Do- load structures exhibit possible channel erosion at their bell, 1961). Name changed from Harrison and Jobin’s margins. Upper contact placed at lowest appearance of (1963) Striped Peak 4 to allow underlying strata to be thin (cm-scale) layers of medium feldspathic quartzite. assigned to the Mount Shields Formation. Unit typically provides poor root support for trees and forms open grassy slopes, although may form prominent cliff outcrops in areas of steep topography, such as those eroded by glacial ice. Well exposed in steep canyon walls on the east side of Dry Creek and the north side of West Fork Elk Creek, and incompletely exposed along the road southeast of Clark Fork, Idaho on the south side of the Clark Fork River. Thickness approximately 90 m (300 ft). Mapped as Striped Peak 3 by Harrison and Jobin (1963). Unit equivalent to the Mount Shields Formation member 6 to the northeast in the Kalispell quadrangle (Harrison and others, 1992).

Figure 17. View northeast at cliffs of Bonner Formation Ybo( ) northeast of the Clark Fork River 4.8 km (3.0 mi) southeast of Clark Fork.

Mount Shields Formation (Mesoproterozoic)—Red, green, and gray quartzite, red and green siltite, red, green, and gray to black argillite, and minor carbonate. Previously assigned to the Striped Peak Formation (Harrison and Jobin, 1963) but reassigned here because strata are more like strata to the east mapped as Mount Shields Formation (Harrison and others, 1992) than strata on Striped Peak southwest of Wallace, Idaho Figure 18. Uneven graded siltite and argillite couplets of

(Lewis and others, 1999). Member numbers are those of member 6 of the Mount Shields Formation (Yms6) south- Harrison and others (1992). east of Clark Fork. Some argillite caps have crinkle cracks similar to those in the Wallace Formation but the rock lacks carbonate. Yms6—Mount Shields Formation, member 6 (Meso- proterozoic)—Rusty weathering, unevenly laminated to planar microlaminated, white to dark greenish gray Yms4-5—Mount Shields Formation, members 4 and 5 siltite and dark greenish gray to black argillite, and rare (Mesoproterozoic)—Tan-weathering, bluish-gray and gray to greenish gray siltite and quartzite in tabular beds bluish-green dolomitic siltite and white stromatolitic as thick as 20 cm. Small and very thin, dark-gray ar- dolomite. Lower part is tan-weathering, bluish-gray gillite chips occur sparsely within some 10-cm-thick and bluish-green and light-green centimeter-scale dark-gray argillite layers. Rare centimeter-wide, long, dolomitic siltite, rare white stromatolitic dolomite and straight cracks and parallel cracks are present, and fine- oolite (Figure 19), and carbonate-poor green, and lesser grained muscovite is common on bedding-plane part- red, siltite and argillite. Salt casts common on green

ings. Includes intervals of soft-sediment deformation argillite parting surfaces. Grades upward from Yms1-3 and truncated laminations throughout the unit. Scour with increasing carbonate and centimeter-thick, rarely channels as wide as 30 cm and as deep as 40 cm com- carbonate-rich siltite with tan weathering rinds, but monly exhibit loaded lower margins and are infilled retains salt casts. Also contains thin layers of “boxwork”

18 Idaho Geological Survey Digital Web Map 189 carbonate and oolite layers 20 cm thick. Distinctive “boxwork” weathering pattern is formed by etching out of resistant, millimeter-thick vertical and horizontal siliceous sheets along joints and cryptalgal laminations (Figure 20). Upward, there are gray- to tan-weathering stratigraphically continuous, prominent resistant gray calcitic or dolomitic “boxwork” carbonate beds, flat algal mats, and rare low domal stromatolites 5 to 10 cm high and 10 to 30 cm across. Weathers recessively, forming topographic benches and poor exposures; commonly represented by float of platy, tan-weathering, centimeter-thick light-green siltite and lag boulders of “boxwork” blocks. Upper contact placed at lowest occurrence of rusty weathering, resistant, laminated dark siltite and argillite of overlying Yms6. Also called members 4 and 5 of the Mount Shields Formation to Figure 20. Calcitic stromatolite with cross-cutting quartz the northeast in the Kalispell quadrangle (Harrison and veinlets in members 4 and 5 of the Mount Shields Formation others, 1992). Thickness approximately 200 m (600- (Yms4-5) along the Dry Creek road south of the Clark Fork 750 ft) and thus more than the 120 m (400 ft) mapped as River. Striped Peak 2 by Harrison and Jobin (1963). Difference Yms —Mount Shields Formation, members 1, 2, in thickness may be partly real and partly from different 1-3 and 3 (Mesoproterozoic)—Pale purplish red, fine- criteria in picking base of carbonate beds in areas of poor grained, flat-laminated quartzite, and green and red exposures. Best exposed in cliffs west of abandoned argillite and siltite; minor carbonate and stromatolites. lookout on Delyle Ridge east of the Twin Creek fault and in roadcuts along the west side of Dry Creek. Coarser grained and thicker bedded in the middle; mudcracks, mud chips, and ripple marks common near base and top; salt casts most common toward the top. Lowest part characterized by 10 to 20 cm beds of green to pink, fine- to medium-grained quartzite and green siltite, both with millimeter-thick green argillite caps. Upward, quartzite is fine to very fine grained, pink, and flat laminated, rarely cross-laminated, in even beds 20 to 30 cm thick, capped by red argillite as thick as 3 cm. Carbonate common near the base in tan-weathering, laminated green dolomitic siltite and light-green argillite intervals, as well as in a few thin tan-weathering quartzite beds. Detrital muscovite flakes generally less than 1 mm across common on partings in the green quartzite. Mudcracks are as deep as 5 cm; mud chips common. Middle is characterized by flat- laminated beds, 30 cm to rare 1 m, of fine- to medium- grained pink to gray quartzite that forms resistant cliffs with blocky talus. Quartzite contains potassium feldspar well in excess of plagioclase and is distinctly coarser than all other quartzite in the area, except the thin sand lags near the base and some beds near the bottom and top of Ybo. Diffuse, nonresistant brown wisps of carbonate within the quartzite average a few centimeters in thickness and 10 to 15 cm in length. Commonly Figure 19. Ooids from members 4 and 5 of the Mount rippled tops of the quartzite beds have thin red argillite drapes. Salt casts increase in abundance upward. Upper, Shields Formation (Yms4-5) along the Dry Creek road south of the Clark Fork drainage. approximately 40 m (130 ft) part of quartzitic interval

19 Idaho Geological Survey Digital Web Map 189 contains numerous 10 cm to 50 dm (rare 1 m) layers Jobin, 1963) and to the south (Lewis and others, 1999, of buff-weathering flat cryptalgal laminated carbonate 2002). Renamed Shepard Formation here because it is and low domal stromatolites as large as 30 cm high and not markedly different from the Shepard Formation at 65 cm across. Also present are scattered beds of oolite its type locality and because it is separated from the 10 cm thick with low-angle internal cross laminations. carbonate-bearing pinch-and-swell strata typical of the Highest part characterized by centimeter- to decimeter- Wallace Formation as found near Wallace, Idaho by scale pink quartzite beds, green and red siltite and carbonate-free dark laminated strata. argillite couples and couplets, and abundant salt casts, mudcracks, and mud chips. There is a general upward Ysh2—Shepard Formation, member 2 (Mesopro- change from centimeter- to millimeter-scale unevenly terozoic)—Rusty weathering, laminated and thinly laminated dark-green siltite and light-green argillite laminated, white, green, and dark-gray siltite and dark- with subordinate decimeter-thick light-green quartzite gray to black argillite, and white siltite and quartzite. to couplets and couples of pink quartzite with thin red Lower part is unevenly laminated light-green to white argillite drapes and subordinate laminated light-green siltite with thin gray to commonly black argillite caps. siltite and argillite, to couplets of light-green siltite and Rare beds as thick as 20 cm of very fine-grained white argillite, with abundant characteristic 10 cm apple-green quartzite contain scattered black mud chips. Rare siltite layers. Throughout the unit are irregular ovoid curved cracks as deep as 5 cm on bedding plane sur- vugs 5 cm across and 3 cm high that commonly contain faces are likely fluid-escape structures. Up section are partial fillings of relict carbonate or secondary silica. 5 to 10 cm beds of slightly dolomitic, dark-green silt- Upper contact placed below increased abundance of ite interstratified with uneven laminae and couplets of carbonate (lowest occurrence of “boxwork” carbonate dark-green siltite and pale-green argillite, identical to or domination of centimeter-scale, tan-weathering lithologies present in Ysh1 (Figure 21). Rare 10 to 20 cm layers of low domal stromatolites. Uppermost part of siltite) in overlying Yms4-5, which commonly coincides with subdued topography or gentle slopes. Best exposed unit unevenly laminated medium greenish-gray siltite in cliff outcrops on west side of Delyle Ridge below and pale greenish-gray argillite similar to lower lith- abandoned lookout. Near the southern edge of the map ologies but lacking carbonate and including rare black east of Mosquito Creek, stromatolitic zones less well argillite. Includes rare 10 cm-thick beds of light-green exposed. Distinguished from Bonner Formation in quartzite and green, decimeter-scale siltite beds. Some having more abundant and better-preserved sedimentary discontinuous centimeter-scale siltite occurs in lenses, structures such as mudcracks and ripples, tan carbonate apparently resulting from soft-sediment compaction. wisps in quartzite, and smaller muscovite flakes on Most continuous section exposed along State Highway bedding partings. Overall thickness uncertain, but 200 southeast of Clark Fork. Incompletely but well ex- approximately 180 m (600 ft) and in agreement with posed on Derr Point. Contact with the overlying Mount the estimate by Harrison and Jobin (1963). Previously Shields Formation is lowest occurrence of centimeter- mapped as Striped Peak 1 (Harrison and Jobin, 1963). scale, very fine grained pink quartzite with red argil- Equivalent to lowest three members of the Mount lite caps or muscovitic forest-green quartzite. Thickness Shields Formation mapped to the northeast in the about 120 m (400 ft) near Derr Point, same as from Kalispell quadrangle (Harrison and others, 1992). Harrison and Jobin (1963). Previously mapped as the laminated argillite and siltite member (Wallace 5) by Shepard Formation (Mesoproterozoic)—Couplets Harrison and Jobin (1963). Equivalent to third member of dolomitic green siltite and light-green argillite, of the upper Wallace Formation to the south (Lewis and dolomitic, dark-gray, very fine grained quartzite, and others, 2002), to upper part of the Shepard Formation laminated and thinly laminated siltite and argillite. in Western Montana (Lemoine and Winston, 1986), and Occupies same stratigraphic level as top of the Wallace to argillite of Half Moon Lake to the north (Miller and Formation previously mapped here (Harrison and Burmester, 2004).

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upper parts, with thin gray non-resistant limestone pods and silty and sandy ripple trains within the thicker argillites. Isolated “starved” ripples common. Upper part is uneven siltite and argillite couples and uneven laminations of slightly dolomitic siltite and argillite. Forms cliffs at some locations, for example, north and northwest of Derr Point; also exposed in lower Derr Creek canyon and northwest of Clark Fork. Upper contact gradational; best placed above highest dolomitic siltite or highest thick dolomitic laminated unit. Thickness about 400 m (1,310 ft) and thus more than the 300 m (1,000 ft) estimated by Harrison and Jobin (1963). Previously mapped as the upper calcareous member (Wallace 4) by Harrison and Jobin (1963). Equivalent to middle unit of member 3 of the Wallace Formation to the south (Lewis and others, 2002), lower part of Shepard Formation present in western Montana (Lemoine and Winston, 1986) and all rocks assigned to Shepard Formation to the north (Miller and Burmester, 2004).

Figure 21. Uneven and locally disrupted microlaminae and graded couplets of calcitic siltite and argillite of member 2 of

the Shepard Formation (Ysh2) east of Clark Fork.

Ysh1—Shepard Formation, member 1 (Mesopro- terozoic)—Tan- and brown-weathering couplets of dolomitic green siltite and light-green argillite with minor Figure 22. Carbonate-rich zone in member 1 of Shepard interstratified 10 to 20 cm beds of dolomitic or calcitic, Formation (Ysh1) south of Clark Fork. very fine grained quartzite. Siltite and argillite are unevenly thinly laminated, microlaminated, and in thin, Ysnw—Snowslip Formation, western facies undi- graded beds (uneven couplets). Uneven laminations vided (Mesoproterozoic)—Rusty-weathering gray of dark-green siltite and pale-green argillite at the base and green siltite and dark-green and gray argillite, sub- pass upward into intervals of thicker uneven couplets ordinate pale-green fine-grained quartzite, and minor of dark-green siltite and pale-green argillite. Weathered carbonate. Gray argillite weathers lighter while accom- outcrops are distinctive brown (siltite) and tan (argil- panying siltite weathers dark rusty red. Green intervals lite) (Figure 22). Dolomite content increases upsection. weather yellowish. Named argillite of Howe Mountain Dolomitic and calcitic quartzite layers as thick as 20 cm on Idaho Geological Survey 7 ½´ quadrangle maps in and rare low domal stromatolite horizons are scattered the Clark Fork area (for example, Burmester and oth- throughout. Layers of flat-pebble rip-up conglomerate as ers, 2004a) to distinguish it from redbed-bearing rocks thick as 5 cm present near middle are commonly associ- in the type section in Glacier National Park. Named ated with centimeter-wide straight cracks that penetrate Snowslip here to simplify stratigraphic nomenclature bedding as deeply as 10 cm through siltite and argillite across the Belt basin but distinguished as western fa- couplets. Bedding locally discontinuous in middle and cies. Corresponds to Snowslip Formation to the north

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(Burmester, 1986; Breckenridge and others, 2014) and monly display distinct, platy talus of smooth, slate-like east (Harrison and others, 1992), and to the lowest part appearance (Figure 23). Similar in plane parallel lami- of the upper Wallace Formation to the south (Lewis nation to the lined unit of the Prichard Formation (Yph) and others, 2002). Subdivided into three units where but not as sulfide rich or rusty weathering. Best exposed exposure adequate. Lowest unit corresponds closely to on ribs east of Johnson Creek. Upper contact relatively the argillite member (Wallace 2) of Harrison and Jobin sharp; placed at top of thick interval of planar laminated (1963). Upper two units correspond closely with the siltite and black argillite. Thickness about 150 m (500 argillite, siltite, and limestone member (Wallace 3) of ft). Mapped as lower part of Wallace 3 by Harrison and Harrison and Jobin (1963). Age of the top of unit is ap- Jobin (1963). proximately that of the Purcell lavas (see Proterozoic igneous rocks, above), which occur close to the Snow- slip-Shepard contact to the northeast and east (Harrison and others, 1992). Thickness about 760 m (2,500 ft). Near Cocolalla, commonly contact metamorphosed, with spots about 1 cm in diameter of uncertain mineralogy increasing to the south. Corresponds to upper Wal- lace member 1 to the south (Lewis and others, 2002) and Snowslip Formation elsewhere; see Burmester and others (2004a) for details.

Ysn3—Snowslip Formation, western facies, member 3 (Mesoproterozoic)—Dark-green siltite and light- green to black argillite as uneven microlaminae and wavy or uneven couplets, and subordinate intervals of unevenly laminated light-gray siltite and black argillite. Thicker green siltite occurs in centimeter- to decimeter- Figure 23. Gray siltite member 2 of the Snowslip Formation thick layers. Black argillite commonly contains small (Ysn2) north of Packsaddle Mountain. Platy parting typical; ptygmatic folds filled with white siltite. Decimeter- plates ring like ceramic when hit. scale green siltite beds are more common than in Ysn1 and Ysn ; black argillite caps less common. Large, 2 Ysn —Snowslip Formation, western facies, member straight-sided cracks, visible on bedding-plane surfaces, 1 1 (Mesoproterozoic)—Uneven couplets to microlami- commonly disrupt lamination to a depth of several nae of gray to green siltite and black, to less commonly centimeters in the green beds. These are interpreted as green, argillite. Some black microlaminated zones show water-escape structures; only near the upper contact soft-sediment deformation. Includes thin zone of planar- are true desiccation cracks and mud chips common. microlaminated siltite and black argillite similar to Ysn Top is gradational into overlying Ysh with increasing 2 1 about 180 m (600 ft) below top. Local straight-sided carbonate content in the interval of microlaminated cracks like in Ysn (Figure 24). Exposed discontinuously dark-green siltite and light-green argillite. Upper contact 3 southwest of Derr Island and west of Packsaddle Moun- placed arbitrarily at lowest appearance of significant tain. Upper contact placed at the base of thick section carbonate within laminated siltite and argillite beds. of planar laminated siltite and black argillite. Thickness Best exposed on ribs east of Johnson Creek. Thickness about 340 m (1,100 ft). Mapped as part of Wallace 3 by about 300 m (1,000 ft). Includes the middle and upper Harrison and Jobin (1963). part of Wallace 2 of Harrison and Jobin (1963).

Ysn2—Snowslip Formation, western facies, member 2 (Mesoproterozoic)—Planar-laminated couplets of greenish-gray siltite and dark-gray to black argillite. Some decimeter-scale gray siltite beds. Charac- teristic plane parallel lamination is widespread at this stratigraphic level (Burmester, 1986; Lewis and others, 1992, 1999, 2002). Thin laminations part evenly on planar bedding surfaces, such that black argillites com-

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that taper downward (Figure 25). On bedding plane surfaces, the cracks are generally discontinuous and sinuous, occurring as isolated parallel or three-pointed star “birdsfoot” cracks (Figure 26). Lower part contains abundant gray- to tan-weathering siltite and black argillite pinch and swell couplets. Beds of distinct “molar-tooth” dolomitic siltite as thick as 30 cm and beds of conchoidally fracturing brown weathering dolomite as thick as 20 cm are locally common. Vertical irregular calcite ribbons and horizontal pods accompany molar tooth structures in some siltite beds thicker than 20 cm throughout the unit. A thin interval of green, dolomitic siltite and argillite and centimeter-scale white quartzite that closely resembles Yhwf is present above Figure 24. Silt-filled straight cracks in siltite and argillite the lowest pinch and swell interval. White quartzite also

couplets of member 1 of the Snowslip Formation (Ysn1) occurs as hummocky cross-stratified tabular beds 15 to along lower part of Johnson Creek road southwest of Clark 30 cm thick; thinner white quartzite beds a few cm thick Fork. Cracks are interpreted as water escape structures. commonly weather with non-resistant vertical joints into a distinct “segmented” appearance. Cycles of 20 to PIEGAN GROUP 30 cm thick white quartzite beds overlain by intervals of microlaminated black argillite are common in upper part. Rare horizons of stromatolites occur in the middle, and Yhw—Piegan Group (Helena and Wallace forma- one thin stromatolite layer occurs near the upper contact. tions), undivided (Mesoproterozoic)—Calcareous Classic exposure along State Highway 200 northwest and non-calcareous very fine grained quartzite or siltite, of Clark Fork. Upper contact placed above highest black argillite, and green dolomitic siltite and argillite. occurrence of pinch and swell couplets. Thickness Shown where lack of mapping or poor exposure prevent about 800 m (2,600 ft). Contact metamorphosed east subdivision. Resurrected by Winston (2007), the Piegan of Careywood. Where metamorphosed, pinch and swell Group provides group-level continuity across the Belt beds are mauve. Zircons from a tuff in the upper Helena basin. It includes only the Helena and Wallace forma- about 170 km (105 mi) east-northeast yielded a U/Pb tions. Excluded from the redefined Wallace (Yw) are up- date of 1,454 ± 9 Ma (Evans and others, 2000), which per members mapped to the south in the past (for exam- may be close to the age of the upper part of the Wallace ples, Harrison and Jobin, 1963; Lemoine and Winston, here. Unit is upper part of the lower calcareous member 1986; Lewis and others, 1999, 2000, 2002). Because (Wallace 1) of Harrison and Jobin (1965). Equivalent to the carbonate-rich strata below the Wallace in most of the middle member of Wallace as mapped by Harrison Idaho are appreciably different from those in the Helena and others (1986, 1992) and Lewis and others (2002). Formation’s new reference section in Glacier National Park, we distinguish these strata as the western facies of the Helena, Yhwf.

Yw—Wallace Formation (Mesoproterozoic)—Pinch and swell couplets and couples of gray, tan-weathering calcareous to dolomitic, very fine grained quartzite, or siltite and black argillite, and lesser amounts of calcareous and non-calcareous white quartzite, dolomitic siltite, and rare stromatolites. Characterized by graded couplets and couples exhibiting pinch and swell sediment type of Winston (1986) in which scours and loads of quartzite cut or deform subjacent black argillite. Black argillite caps commonly contain ptygmatically folded siltite- or quartzite-filled cracks

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weathering, green silty dolomite or dolomitic siltstone. Quartzite typically exhibits vertical segmentation gaps where carbonate was removed. Brown-weathering, gray, conchoidally-fracturing dolomite scattered throughout; gray limestone with characteristic vertical “molar- tooth” structures common. Oblong horizontal carbonate “pods” (Figure 28) within the silty dolomite are more abundant higher in unit. Gray quartzite with black argillite caps containing ptygmatically folded crack fillings and massive black argillite in thin beds are more common near the top. Best exposed along old Highway 200 northwest of Clark Fork. Upper contact placed at lowest concentration of pinch and swell couplets with black argillite tops. Thickness uncertain but on the Figure 25. Pinch-and-swell couples and couplets of very fine order of 240 m (800 ft) west of Clark Fork, and 260 quartzite (light) and argillite (dark) of the Wallace Forma- m (850 ft) west of Lake Pend Oreille. Corresponds to tion (Yw) east of Denton Slough. Uneven bases from load but differs sufficiently from the Helena Formation to the and scour, plus irregular, distorted quartzite- or siltite-filled east (Harrison and others, 1992) to be a different facies. cracks in argillite (crinkle cracks) are typical of this forma- Lowest 100 m (330 ft) possibly equivalent to Empire tion. Hand lens for scale. Formation. Zircons from a tuff in the upper Helena about 170 km (105 mi) east-northeast yielded a U/Pb date of 1,454 ± 9 Ma (Evans and others, 2000). Unit is lower part of the lower calcareous member (Wallace 1) of Harrison and Jobin (1963). Equivalent to the lower member of Wallace as mapped by Harrison and others (1986) and Lewis and others (2002).

Figure 26. Bedding surface of Wallace Formation Formation (Yw) east of Denton Slough showing light-colored siltite filling isolated “crinkle” cracks in dark argillite caps.

Yhwf—Helena Formation, western facies (Mesoproterozoic)—Cyclic couplets and couples of white quartzite to tan-weathering dolomite or dolomitic Figure 27. Thin, wavy laminae to uneven couplets of siltite, with associated massive green siltite and thinly green siltite and light-green argillite along with molar-tooth laminated, uneven green siltite and argillite couplets structure in western facies of the Helena Formation (Yhwf) containing various amounts of carbonate (dolomite) southeast of Denton Slough. and calcite pods. Lower part predominately thin, wavy laminae to uneven couplets of green siltite and light- green argillite (Figure 27). Upper part dominated by siliciclastic to carbonate cycles. White calcitic quartzite, commonly 10 to 20 cm thick, overlain by tan-

24 Idaho Geological Survey Digital Web Map 189

Figure 28. Carbonate pods in western facies of the Helena Formation (Yhwf) southeast of Denton Slough. Figure 29. Block of quartzite from St. Regis Formation (Ysr) west of Lake Pend Oreille near Blacktail Mountain with well-rounded medium quartz grains. Concentrations of simi- RAVALLI GROUP lar anomalously large grains occur in members c and e of the Prichard Formation (Ypc, Ype) and in the Bonner Formation. Ysr—St. Regis Formation (Mesoproterozoic)—Red to pale-purple to gray siltite, argillite and quartzite, light- green siltite and darker green argillite or dark-green siltite and light-green argillite couplets. Over Blacktail Mountain base includes apparent lag deposit of well- rounded medium quartz grains (Figure 29). Red color is local to west of Lake Pend Oreille, perhaps due to lower metamorphic grade there. Green is more common near top. Mudcracked siltite and argillite couplets are characteristic (Figure 30). Less common are very thin (2 to 5 cm) and rarer thin (10 to 20 cm) tabular fine-grained quartzite beds with green argillite caps, similar to those of Yr. Tabular quartzite beds particularly abundant near base. Conspicuous layers of mud chips as thick as 5 cm ubiquitous. Thin (millimeter-scale) wisps of brown- Figure 30. St. Regis Formation (Ysr) quartzite, siltite, and weathering dolomitic siltite more common within the argillite with mudcracks and chips west of Lake Pend Oreille siltite and argillite couplets in upper part. Wavy couplets near Blacktail Mountain. and couples with purple siltite and green argillite as thick as 20 cm common toward top. Best exposed on Yr—Revett Formation (Mesoproterozoic)—Resis- cliffs near Sheepherder Point southwest of Denton tant white to pale-purple or rarer light-green quartzite Slough. Upper contact placed above the highest cracked with green siltite and argillite, commonly as millimeter and mud chip-bearing purple siltite and argillite, where to centimeter green, locally purple argillite caps. Most the carbonate-bearing wavy green siltite and argillite beds tabular, although wedge-shaped or discontinuous laminae and couplets of overlying Yhwf succeed them. beds are common. Some quartzite vitreous or sericitic; Thickness about 240 m (800 ft) south of Hope, and 550 most feldspathic with subequal potassium feldspar and m (1,800 ft) near Maiden Creek east of Cocolalla. (600 plagioclase, each comprising 15 to 20 percent of the to 1,000 ft; Harrison and Jobin, 1963). Some of the rock. Some weathers orange; orange-brown spots less difference in thickness is attributable to our exclusion than 1 mm in diameter common; attributed to weather- of purple strata from Yhwf whereas Harrison and Jobin ing of ferroan carbonate (Garlick, 1988). Rippled tops (1963) included some in their lower calcareous member (Figure 31) and tabular planar cross-lamination more (Wallace 1). common than trough cross-lamination; much is flat

25 Idaho Geological Survey Digital Web Map 189 laminated. Quartzite is commonly of the discontinuous sediment type, containing irregular internal argillite wisps. Mudcracks and mud chips common in argillitic tops throughout unit. Lower part consists of multiple beds of feldspathic quartzite more than 30 cm thick (cosets of thick sets). Middle part is a less-resistant interval with lower concentration of quartzite and more mudcracked couplets of pale-purple or green siltite and dark-purple or green argillite. Upper part consists of more cosets of thick sets of resistant quartzite (Figure 32), with thin cracked green argillite caps. Load casts as large as 20 cm deep and 30 cm across (Figure 33) and small ball and pillow structures are especially abundant in the upper part, although present at the bases of some quartzite beds throughout. Most continuously exposed on west slope of Blacktail Mountain. Where adequately exposed, upper contact placed above highest Figure 32. Thick quartzite beds, upper Revett Formation (Yr) cosets of thick sets of quartzite. Placement of contacts west of Lake Pend Oreille on the northeast side of Maiden likely different from previous mapping because we fol- Creek. lowed Hayes (1983; Hayes and Einaudi, 1986) in using physical attributes of quartzite and not color to specify the unit's contacts. Where outcrops sparse, unit characterized by decimeter to multi-decimeter float or talus of light-weathering quartzite. Thickness about 550 m (1,800 ft) near Hope, and 760 m (2,400 ft) near Maiden Creek east of Cocolalla.

Figure 33. Load cast base of thick quartzite of the Revett Formation (Yr) east of Denton Slough.

Yb—Burke Formation (Mesoproterozoic)—Green siltite and argillite and gray to white to purple mottled quartzite (Figure 34). Siltite beds typically 10 to 20 cm with sub-millimeter macroscopic magnetite octahedra. Argillite partings commonly dark green, some lighter green. Contact metamorphism in south-central part of the map is probably responsible for loss of colors and schistosity of argillitic parts. Mudcracks and chips common throughout. Flat-laminated, fine-grained, gray to white quartzite in 20 to 50 cm beds, some with rippled tops and cross-lamination, are present toward bottom and increase upward. Nearly spherical manganese carbonate concentrations common within quartzite Figure 31. Asymmetric current ripples on top of bed in weather to round or ellipsoidal spots or cavities 4 to Revett Formation (Yr) west of Lake Pend Oreille on the 8 cm across. Purple-banded quartzite in beds 20 to 50 northeast side of Maiden Creek. cm thick common near top. Discontinuously exposed

26 Idaho Geological Survey Digital Web Map 189 on west slope of Blacktail Mountain and west and carbonate “pods” occur as round to oblong, brown- southwest of there. Upper contact placed at base of weathering spots or cavities 5 to 15 cm in diameter. lowest cosets of thick sets of quartzite of Yr where well Sedimentary structures such as incipient and polygonal exposed, or at lowest occurrence of abundant float of cracks, ripples, and mud chips are common on argillitic white quartzite where not. Thickness 1,000 m (3,300 ft), surfaces of bedding plane partings throughout. similar to that reported Harrison and Jobin (1963). Ptygmatic folding of siltite crack filling indicates cracks formed in wet mud. Best exposed west of Scotchman Peak. Upper contact placed above highest recognized pinch and swell couplets with dark-gray argillite tops. Inclusion of some quartzite at top where dark argillite persists but is a minor component probably accounts for higher placement of contact and greater thickness (500 m, 1,640 ft near Derr Point, and 450 m, 1,480 ft near Sagle) than in previous mapping (245 to 305 m, 800 to 1,000 ft; Harrison and Jobin, 1963). Greater thickness to north (640 m, 2,100 ft; Burmester, 1986) is not attributable to different contact criteria. Mapped here as “transition zone” into overlying Burke Formation whereas elsewhere included in Burke (for example, Cressman, 1985).

Figure 34. Burke Formation (Yb) west of Lake Pend Oreille on northeast side of Maiden Creek. Note typical gray color and weathering rind.

PRICHARD FORMATION

Ypt—Prichard Formation, transition member (Mesoproterozoic)—Gray to greenish-gray to white siltite and dark-gray argillite couplets, with scattered white quartzite beds at base and top. Overall, bedding Figure 35. Uneven graded couplets of Ypt, the highest mem- uneven, with slight loading or channeling at bed or ber of the Prichard Formation. Photo from east of Cocolalla couplet bases common. Some siltite beds as thick as Lake. 10 cm have no discernable internal structure. Siltite also as bases of microlaminae and pinch and swell Yph—Prichard Formation, member h (Mesopro- couplets with white siltite grading upward to dark- terozoic)—Laminated gray siltite and black argillite gray siltite, less commonly argillite (Figure 35). Dark, couplets to microlaminated black and white argillite. sub-millimeter grains within siltite appear to be biotite Laminae and microlaminae characteristically very even low in unit, but magnetite toward the top as the siltite and continuous and not graded (Figure 36). This is nick- beds become greener. White quartzite beds 10 to 50 named the “lined unit” of the Prichard Formation. Part- cm (rarely 1 m) are present at the base of the unit and ing commonly 2 mm to 3 cm, although parting absent scattered throughout the lower part. Quartzite very fine in some places where unit weathers into large boulders. grained and characterized by dark, millimeter planar Weathers with a distinct rusty veneer and is a resistant laminations, as well as common ripple and larger low- cliff-forming unit in the area. Best exposed west of Goat angle cross-laminations, small “dish” structures, and Mountain. Upper contact placed at the lowest occur- scattered load structures as deep as 15 cm. Manganese rence of white quartzite beds and wavy siltite and dark

27 Idaho Geological Survey Digital Web Map 189 argillite couplets of overlying Ypt. Thickness of about 580 to 700 m (1,900 to 2,300 ft) is similar to that reported by Harrison and Jobin (1963) and between thicknesses of unit to the southeast (1,450 to 1,770 m; 4,760 to 5,810 ft; Cressman, 1985) and north (370 m, 1,200 ft; Burmester, 1986).

Figure 37. Thick quartzite beds of member g of the Prichard Formation (Ypg) on the west shore of Lake Pend Oreille near Talache.

Figure 36. Even, parallel-laminated siltite characteristic of member h of the Prichard Formation (Yph). Photo from Pearl Island, southwest of Hope.

Ypg—Prichard Formation, member g (Mesopro- terozoic)—Gray to white feldspathic quartzite and dark-gray argillite. Quartzite fine to very fine grained in 1 to 3 dm, rarely thicker beds (Figure 37). Rare medium grains occur scattered in the finer grained matrix low in some beds. Ripple cross-lamination and rippled tops present though not abundant, as are load and scour features at bases of quartzite beds, and rare (mud?) cracked argillite tops. Interlayered with platy (Figure 38), even parallel laminated siltite as well as uneven couplets of light-gray to white siltite and black argillite. Well exposed west of Goat Mountain. Top placed below thick interval of flat-laminated dark siltite and argillite. Thickness of approximately 560 m (1,750 to 1,950 ft) is similar to thickness to the southeast (500 m; 1,640 ft; Figure 38. Platy parting siltite of member g of the Prichard Cressman, 1985) and north (610 m; 2,000 ft; Burmester, Formation (Ypg) east of Moose Lake in the northeast part of 1986). the map.

28 Idaho Geological Survey Digital Web Map 189

Ypf—Prichard Formation, member f (Mesoprotero- anomalously thin relative to other areas. More likely the zoic)—Gray siltite dark-gray argillite couplets, lami- unit is repeated by mapped and unmapped, down-to- nated light-gray and dark-gray siltite, and minor lighter the-west normal faults and perhaps northwest-vergent quartzite. Siltite rusty weathering, with lamination and thrust faults. It seems plausible that the Lightning Creek parting typically thicker than in Yph. Most lamination is stock intruded one or more such faults. planar, although 3 to 10 mm scours, cross-lamination, load features, and minor hummocks are present in the light siltite bases of wavy to irregular couplets scattered throughout (Figure 39). Quartzite beds tend to be 5 cm to 3 dm in thickness, very fine grained, and light gray. Some have scoured or loaded bases (Figure 40).

Figure 40. Bottom mark flute casts, member f of the Prichard Formation (Ypf) on Moose Mountain, above middle east side of map.

Ypfq—Prichard Formation, member f quartzite (Mesoproterozoic)—Light gray weathering, medium- grained quartzite mapped as individual intervals in well-exposed parts of the aerial distribution of Ypf. Only subdivided locally from Ypf by use of hanging contacts. One sample low in Ypf lacked potassium feldspar and had approximately 5 percent plagioclase. Two samples from a thick quartzite interval higher in Ypf have what appears to be late secondary or authigenic potassium feldspar, possibly due to intrusion of the Lightning Figure 39. Unevenly laminated siltite of member f of the Creek stock and related dikes. Locally contains brown Prichard Formation (Ypf) on west side of Lake Pend Oreille weathering ovoid carbonate concretions as large as 30 east of Garfield Bay. cm in diameter. Forms resistant ridges. Only north of Clark Fork, north and south of the Lightning Creek Contains metamorphic biotite and chloritoid. Unit re- stock, where some may be fault repeated. ported to contain argillite pebble conglomerate to the southeast (Cressman, 1985). Exposed across Callahan Ype—Prichard Formation, member e (Mesopro- Creek as well as over Bee Top Mountain. Upper con- terozoic)—Light gray to white weathering siltite and tact placed below concentration of feldspathic quartz- quartzite and darker argillite. Siltite dominates over very ite beds of Ypg. Thickness near Callahan Creek (1,100 feldspathic quartzite, but both exhibit features of current m; 3,600 ft) is similar to thickness about 145 km (90 traction such as rippled tops and ripple cross-lamination mi) to the southeast (989 to 1,100 m; 3,200 to 3,600 ft; (Figure 41). Soft-sediment deformation features com- Cressman, 1985) and closer to the north (910 m; 3,000 mon; locally abundant load casts and ball and pillow ft; Burmester, 1986), The swath mapped across Light- structures. Quartzite and siltite commonly parallel lami- ning Creek requires a thickness of 3,000 m (9,800 ft). nated to structureless; rare trough to low-angle cross- This thickness is not due to differences in contact place- bedding. Some quartzite beds coarser grained and less ment, given that overlying and underlying units are not feldspathic than typical of the Prichard. Four samples

29 Idaho Geological Survey Digital Web Map 189 from north of Hope and Clark Fork lacked potassium feldspar and have approximately 5 to 10 percent plagioclase. These are poorly sorted but contain well-rounded, spherical, medium quartz grains. Better sorted, similarly shaped large grains form matrix of rare, decimeter-thick intraclast conglomerate beds at a few horizons high in the unit. Quartzite-rich sections commonly form bare resistant ribs and talus slopes. Best exposed on ridge over Round Top and Smith Mountain. Upper contact placed above highest zone of quartzite with abundant current features and below a thick section of uniformly parallel-laminated rusty-weathering siltite. Thickness approximately 700 m (2,300 ft excluding 300 m of sills) (820 m, 2,700 ft excluding sills; Cressman, 1985). Figure 42. Parallel-laminated siltite of member d of the Prichard Formation (Ypd) southeast of Hope. Member has abundant marker beds, is sulfide rich, quartzite poor, and thin bedded in comparison to underlying and overlying members.

Ypc—Prichard Formation, member c (Mesoprotero- zoic)—Dark- to medium-gray siltite, dark-gray siltite and argillite couplets, and light-weathering quartzite. Finer-grained material unevenly laminated and rusty weathering. Fine-grained to rare medium-grained quartzite scattered throughout is similar to that of Ype but occurs in thinner beds (Figure 43). Feldspar content varies, ranging from 5 to 25 percent. Plagioclase more abundant than potassium feldspar; the latter is lacking in many of the samples collected. Some potassium feldspar may be secondary. Some beds preserve ripples Figure 41. Rippled quartzite of member e of the Prichard and cross-lamination, coarser grains at bases and grada- Formation (Ype) exposed above Crossport C mafic sill tion to siltite at the top. Rare quartzite beds as thick as 2 (Ymic) on Smith Mountain in the northeast corner of map. m with medium- to granule-size grains in 20 cm basal lags. Anomalously coarse quartz grains also comprise Ypd—Prichard Formation, member d (Mesopro- the matrix of associated rare, decimeter-thick intraclast terozoic)—Light-gray siltite and dark-gray argillite. conglomerate beds at a few horizons. Intraclasts are as Most is unevenly laminated couplets but there are abun- large as 5 cm long and 3 cm thick, commonly deformed dant intervals of thinner, even parallel laminated, rusty and arranged roughly parallel to bedding. Intraclast weathering, dark-gray to white siltite and dark-gray lithologies in decreasing order of abundance include argillite couplets and micolaminae. (Figure 42). Less black argillite, laminated siltite and argillite, and coarse common are scattered 1 to 3 m thick intervals of white, sand. Circular brown spots 2 to 6 cm in diameter with very fine- to fine-grained quartzite in rare cosets of 1 to alteration “halos” probably reflect original localization 3 dm white, rusty-weathering siltite. Exposure gener- of magnesium carbonate. Hosts one or two undifferenti- ally poor and discontinuous, with quartzite commonly ated sills. Quartzite well exposed locally where it holds over-represented in float. Perhaps best exposed west of up ridge tops and on steep slopes; finer-grained parts are Round Top Mountain. Upper contact placed at lowest exposed best near quartzite, especially on ridges. Best occurrence of current-laminated siltite and quartzite in exposed near head of Trestle Creek and on Lunch Peak. the interval occupied by one or more thick, differenti- Top placed above set of quartzite beds and below thick ated sills. Thickness approximately 340 m (1,100 ft). In interval of more evenly laminated siltite and argillite. the Plains, Montana area member d is 280 m (920 ft) Thickness across Trout Peak estimated at 1,000 m (3,400 of platy weathering olive-gray silty argillite (Cressman, ft) including a sill; slightly thicker section across Mount 1985). Eagan (1,100 m; 3,600 ft) may be inflated by a second

30 Idaho Geological Survey Digital Web Map 189 sill, or fault repetition of one. In the Plains, Montana and argillite with possibly one quartzite interval and a area, member c is 75 to110 m (250 to 360 ft) of very fine- mafic sill that was used to divide b from a (Cressman, grained argillitic quartzite and intercalated siltite and 1985). Ypab east and southeast of Elmira is thick argillite (Cressman, 1985). and may extend down-section farther than Prichard units around Trout Peak where stratigraphy is better constrained by confidence in recognition of Ypc above Ypab (Lewis and others, 2006a). May also extend lower than Plains, Montana, section described by Cressman (1985).

Figure 43. Quartzite of member c of the Prichard Forma- tion (Ypc) on the northwest side of Smith Mountain, northeast corner of map. Ypab—Prichard Formation, members a and b (Mesoproterozoic)—Dark-gray siltite and argillite Figure 44. Highly stained siltite of Prichard members a and couplets, dark-gray siltite, and rare lighter quartzite. b, (Ypab) north-northwest of Priest River. Staining attributed Most is rusty weathering (Figure 44). Couplets typically to weathering of sulfides present in high concentration. not graded, planar laminated, and less than one cm thick; argillite tops locally light weathering. Siltite layers, both 1 to 5 cm and 1 to 5 dm, are generally dark gray, some Ypm—Prichard Formation, massive unit weathering light gray. Light-gray to white weathering (Mesoproterozoic)—Structureless, poorly sorted quartzite as 1 to 3 dm separate beds; 2 to 10 dm beds quartzite and siltite. Some superficially resembles in cosets 2 to 5 m thick are more common toward top. fine-grained granodiorite, but generally has too much Intimately associated with Ypm; whether slump folds quartz. Found as irregularly shaped bodies near the top (scattered orientations lacking axial plane cleavage), of Ypab. Associated with mafic sills and layered rock convolute bedding, and intraformational conglomerate with soft-sediment deformation and slump folds with of contorted, irregular clasts are typical of part of Ypab wavelengths as great as 30 m (100 ft); has indistinct or mark a transition between Ypab and Ypm is unknown. contacts with both. Locally contains 5 percent clasts of Inconsistency of cleavage development across the area laminated siltite and argillite 1 to 3 cm thick and 5 to 30 suggests local rather than regional influence. Unit hosts cm long, and less commonly quartzite balls or blocks. Moyie sills that range from tabular with differentiated Clasts commonly have apparent reaction rims and tops to irregular with no differentiation. Well but some appear deformed (Figure 45). Massive granofels- discontinuously exposed on steep slopes and ridge tops. like texture with fine biotite common. Similar rock to Most easily seen along State Highway 200 between the north contains abundant granophyre (Redfield, Hope, Idaho and Trestle Creek, less accessible across 1986), blurring the distinction between igneous and Calder Mountain near the northern map boundary. Top metamorphic origin. May have formed from increased placed at base of section of relatively abundant quartzite pore fluid pressure due to heating by the sills (Anderson beds 3 to 10 dm thick that contains well-rounded and Höy, 2000) or from water-rich fluids that had medium quartz grains and preserved ripples and cross- separated from an underlying sill (Poage and others, lamination. In the Plains, Montana area, members b and 2000). Weathers rustier than quartzite of Ype or Ypc. a are about 1,600 m (5,250 ft) of interlaminated siltite Generally hardest rock of the Prichard Formation,

31 Idaho Geological Survey Digital Web Map 189 forming rounded exposures and large blocky talus. PRIEST RIVER COMPLEX Well exposed north of Trestle Creek and over Purdy METASEDIMENTARY ROCKS Mountain. Small bodies not mapped separately from Ypab, for example, west of the East Newport fault. Amphibolite facies metasedimentary rocks are exposed between the East Newport and Purcell Trench faults within the Priest River metamorphic complex. Detrital zircon ages indicate that their protoliths are likely the same age as the Belt Supergroup (Doughty and Chamberlain, 2008). However, peak metamorphism in and near the southwest corner of the map was 74 to 54 Ma, whereas crystallization of leucocratic melts may have been 54 to 44 Ma (Stevens and others, 2015). Ygs—Gneiss and schist (Mesoproterozoic)—Musco- vite-biotite-plagioclase-quartz gneiss, muscovite-biotite schist, biotite-muscovite schist, and minor graphite- biotite-quartz-feldspar granofelsic gneiss and garnet- graphite-feldspar quartzite. Rusty weathering common. Layering on centimeter scale may be relict bedding. Sil- Figure 45. Deformed and disrupted bedding in laminat- limanite is common. Podiform segregations of granitic ed and massive siltite of massive unit of the Prichard material (Figure 47) are abundant, and the widespread Formation (Ypm) west of Callahan Creek near Purdy presence of potassium feldspar and sillimanite are consistent with peak metamorphism above the breakdown Mountain in the northeast corner of the map. reaction of quartz + muscovite. Kyanite is rare, being Ypmt—Metamorphosed Prichard Formation (Me- found only near Prater Mountain. Near there, lath- soproterozoic)—Biotite quartzite and metamorphosed shaped sillimanite aggregates suggest that kyanite was siltite exposed in and east of the Purcell trench north part of a prograde assemblage, not the peak metamor- and south of Sandpoint. East of Elmira, unit is quartz- phic assemblage (Stevens and others, 2015). Doughty biotite-muscovite schist grading to gneiss, and feld- (1995) calculated peak metamorphic pressures between spathic muscovite-biotite quartzite. Typically contains 7 and 9 kbar for these rocks based on the simultaneous lenses of muscovite 5 to 10 cm long (Figure 46). Prob- solution of the garnet-Al silicate-plagioclase (GASP) ably equivalent to Ypab described above, but metamor- barometer and garnet-biotite thermometer. More recent phic grade is higher and rock is more coarsely recrystal- results (Stevens and others, 2015) outline southward lized. Likely equivalent of Ygs, but lower metamorphic increase in peak temperature and pressure from about grade and less deformed. 6.4 kbar and 700°C 4.4 km (2.7 mi) north of Sundance Mountain (east of Priest Lake) to 10.0 kbar and 800°C 4.4 km (2.7 mi) south-southeast of Blanchard. Pegma- tite-rich west of Elmira where massive pegmatite bodies 10 to 30 m (33 to 100 ft) thick form cliffs and large talus blocks within muscovite-biotite-plagioclase-quartz gneiss, biotite-muscovite schist, and muscovite-biotite schist. Schists also contain quartz and plagioclase. In- cluded in “mixed granitic and metamorphic rocks of Soldier Creek” by Miller and others (1999). Includes unmapped granitic sills, pegmatite bodies, and amphibolite, locally with garnet as large as 2 cm, and (or) biotite replacing hornblende. Unit is considered equivalent to the Hauser Lake gneiss (Weis, 1968; Weisenborn and Weis, 1976) and was considered metamorphosed Prichard Formation by Miller and others (1999). De- Figure 46. Elongate lenses of muscovite interpreted as trital zircon age spectrum from a sample southwest retrograde sillimanite in metamorphosed Prichard Formation of Laclede, and zircon ages from nearby amphibolite, (Ypmt). support derivation of the Hauser Lake gneiss from the

32 Idaho Geological Survey Digital Web Map 189

lower Prichard Formation (Doughty and Chamberlain, Yq—Quartzite (Mesoproterozoic)—Biotite-feldspar 2008) as does the spectrum from a sample from east of quartzite that occurs as small bodies within Ygs. Coolin (Lewis and others, 2010). Ages from metamorphic zircon rims from Laclede sample (1,304 ± 32 Ma; Ycs—Calc-silicate rocks (Mesoproterozoic)—Mylo- Doughty and Chamberlain, 2008) and garnet growth nitic graphite-plagioclase-pyroxene(?) quartzite that oc- age from equivalent rock 23 km (14 mi) to the south curs as small bodies within Ygs. (1,379 ± 8 Ma; Zirakparvar and others, 2010) support Ygq—Granofels and quartzite (Mesoproterozoic)— extensive metamorphism during the East Kootenai Biotite-quartz-feldspar granofels and feldspathic biotite and (or) Grenville orogenies. Spectacularly exposed in quartzite all with or without muscovite. Granofels has State Highway 200 road cuts northeast and southwest gneissic layering but lacks a strong foliation. Most if of Laclede (Figure 48). Note that if Yag (below) is on a not all feldspar is plagioclase. Contains garnet on the major thrust, Ygs strata above it likely originated much south side of Berry Creek west-northwest of Colburn. farther west in the Belt basin than those below. Unit is more widely exposed near Mt. Casey to the west where it also contains thin intervals of calc-silicate rock. Near Colburn, is mostly layered biotite-quartz-feldspar granofels and feldspathic biotite quartzite. Near Elmira, consists of biotite-muscovite-quartz-feldspar granofels, feldspathic biotite quartzite, and muscovite-biotite- feldspar-quartz gneiss. Similar to gneiss and schist unit (Ygs) but more quartz rich. Includes unmapped amphibolite and granitic sills. Location suggests unit is probably metamorphosed Prichard Formation, but detrital zircon U/Pb dating results from a sample from Mt. Casey show fewer grains with non-North American ages (1,610 to 1,490 Ma) and more Archean grains than found in typical Prichard samples (Lewis and others, 2010). YXqgc—Quartzite of Gold Cup Mountain (Paleo- proterozoic or Mesoproterozoic)—Coarsely recrystallized quartzite. Contains 80 to 93 percent quartz, 0 to 27 Figure 47. Granitic segregations in gneiss and schist unit percent potassium feldspar, 0 to 6 percent plagioclase, 1 (Ygs) south-southwest of Priest River. to 3 percent biotite, 1 to 8 percent sillimanite, and 0 to 3 percent magnetite. Detrital zircons are not younger than 1,800 Ma (Doughty and Chamberlain, 2008). BASEMENT ROCKS

Yag—Augen gneiss (Mesoproterozoic)—Well-foliated biotite granite augen gneiss exposed in fault- bounded slices within a domal structure southeast of Priest River (Figure 49). Sub-equal amounts of potassium feldspar and plagioclase and 4 to 13 percent biotite. Low magnetite content in two samples and high magnetite content in one sample (Table 1). Included in gneiss of Laclede by Miller and others (1999). Age is 1,576 ± 13 Ma (Evans and Fischer, 1986; Doughty and others, 1998). Note that this falls within the 1,610 to 1,490 Ma "North American magmatic gap", a time Figure 48. View north-northwest of gneiss and schist unit period in which igneous activity in Laurentia was rare (Ygs) above augen gneiss (Yag) west of Laclede. (Ross and others, 1992). Unit may thus represent part of a land mass largely rifted away (Australia?) at the end

33 Idaho Geological Survey Digital Web Map 189

of the Proterozoic. Its lower fault contact is interpreted the East Newport fault are exclusively lower Prichard as a major Cretaceous thrust, possibly the basal décolle- Formation and intrusions. Those rocks are faulted ment of the Sevier thrust belt envisioned by Rhodes and and folded in a south-plunging anticline, but the west Hyndman (1984) for the Spokane dome mylonite zone, flank of the anticline continues up section to the West which is above this fault. Most accessible along State Newport fault in the adjacent Chewelah quadrangle and Highway 200 southwest of Laclede. includes strata above the Belt Supergroup (Miller, 2000). Rocks to the east of the Purcell Trench fault comprise a similar homoclinal sequence through most of the Belt Supergroup. Repetition and structural thickening of some units may be due to growth faulting during deposition, extensional faulting during Windermere rifting, thrust faulting during Cretaceous shortening, and normal faulting during Eocene extension. This discussion will examine structures on this map in roughly chronological order.

PROTEROZOIC FAULTING

Some faulting likely accompanied formation of the Belt basin as an intracratonic rift (Sears and others, 1998; Chandler, 2000; Sears, 2007). Activity during Figure 49. View north-northwest of augen gneiss (Yag) west deposition of the Prichard Formation may account for of Laclede showing top-to-the-east-northeast kinematic S-C difference in thickness of mafic sills across it (Harrison fabric. and Jobin, 1963). However, the Hope fault appears to have posed no barrier to the Ydb sill near the bottom of Wgn—Biotite gneiss (Archean)—Biotite granodiorite Yb, which is found with similar thickness and at the same gneiss and layered quartzofeldspathic biotite gneiss that stratigraphic level both north (near Scotchman Peak) may be metasedimentary in origin. Granodiorite gneiss and south (both sides of Owens Bay) of the fault. Nor is foliated, and contains roughly 20 to 22 percent quartz, are thicknesses of Belt Supergroup units significantly 12 to 15 percent potassium feldspar (in layers), 50 to 58 different on either side of the Hope fault. Faulting percent plagioclase, and 10 to 15 percent biotite. High through the end of Belt deposition is documented about magnetite content in two orthogneiss samples (Table 1). Age is 2,651 ± 20 Ma (U-Pb; Doughty and others, 175 km (110 mi) north of Sandpoint in the Purcell 1998). Mountains of British Columbia (Gardner, 2008), so it is likely that the duration of faulting was similar for the Sandpoint area. STRUCTURE

The major structure in the Sandpoint area is a broad anticline of mostly low metamorphic grade Belt Supergroup rocks cored by the Priest River complex (PRC) of higher grade and more deformed lowest Belt and older rocks (Figure 50). The PRC is bounded on the west by the East Newport fault and on the east by the Purcell Trench fault. Plutonic igneous rocks are concentrated within the PRC and adjacent to it. Those within (Priest River complex intrusive suite) typically are foliated to mylonitized; those outside (high-level intrusive suite) are typically not deformed. Low-grade rocks within the Sandpoint quadrangle to the west of

34 Idaho Geological Survey Digital Web Map 189

117˚ 116˚

0 25 mi 0 50 km Creston Yb Ym BC Yb BC 49˚ Purcell Trench MT fault

East Newport Yb Bonners fault Ferry

PRC Pack West River

ID Newport WA fault this fault map Ym

Yb PRC

Sandpoint Hope Yb Ym Yb

XAb fault

fault 48˚ Spokane dome Ym

Magee Cascade fault zone CDA Yb

Spokane Ym Osburn fault XAb PRC

Yb Purcell Trench St. Joe fault fault Yb Yb Yb

Rocks and deposits post-dating High-angle normal fault the Belt Supergroup Strike-slip fault Yb Belt Supergroup Low-angle normal fault Ym Metamorphosed Belt Supergroup Upper contact of Spokane XAb Basement rocks dome mylonite zone

Figure 50. Regional structural map emphasizing the Priest River metamorphic complex (PRC) and the overlying Belt Supergroup. Modified from Doughty and Price (2000) and Doughty and others (2016).

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NEOPROTEROZOIC dips suggests that it possibly accommodated shortening inside a large, eastward vergent syncline defined by the (WINDERMERE) FAULTING shallower dips to the east and steeper dips to the west. Apparent termination of this fault and zone of steep dips Differential erosion of Belt strata before accumulation to the north suggests that the Hope fault or another fault of Paleozoic shelf sediments is demonstrated within and south of it acted as a transform fault during thrusting. adjacent to the Sandpoint area. Basal middle Cambrian Near the Hope fault, we found shears parallel to bedding quartzite sits on slightly different parts of the Snowslip planes on Antelope Mountain east of Clark Fork, Formation west of Packsaddle Mountain and on middle although did not determine kinematics. These may be Mount Shields Formation strata 100 km (62 mi) to the related to the northwest-vergent thrust faults mapped in southwest, about 5 km (3 mi) south of the map. This and around mines north of Clark Fork, which appear to variation is most easily explained if the Cambrian strata be earlier than the steep, extensional faults that control around Packsaddle Mountain were deposited on a tilted mineralization (Anderson, 1947). The shears and faults fault block, which was separated from rocks south of likely date from Cretaceous contraction. Although these the map by a Neoproterozoic fault with a component faults have small displacement and are not shown on of motion down to the south. However, Belt rocks were the present map, there may be others that are not well not as deeply eroded both to the east and west before exposed that have more displacement and duplicate Paleozoic time. Cambrian rocks, possibly on top of some parts of the section, specifically of the Shepard weathered Windermere, are reported on top of the Libby Formation west of Clark Fork, and Prichard unit Ypf Formation 110 km (70 mi) to the southeast of Sandpoint across and west of Lightning Creek. Small folds and (Retallack and others, 2003). Paleozoic strata rest disparate attitudes around the Lightning Creek stock unconformably on Bonner Formation strata less than 20 have been attributed to its intrusion (Harrison and Jobin, km (12 mi) west of the map. Farther west on Quartzite 1963; Fillipone and Yin, 1994) but it is conceivable that Mountain east of Chewelah, Washington, about 80 km an early thrust fault along Lightning Creek accounts (50 mi) west of Sandpoint, they rest on Libby Formation for some deformation and accommodated the stock. If rocks (our reconnaissance with F.K. Milller, 2006). One true, lack of fabric in the stock indicates that thrusting interpretation of this difference is that a broad, faulted there had ceased by 74 Ma (see Khgd description). A arch with culmination near the present Purcell Trench possibly younger, brittle, west-dipping fault north of the developed during the Neoproterozoic and was eroded map (Burmester and others, 2009) has drag folds and before the Paleozoic. Reactivation of the responsible offset contacts indicating east vergence. Another, east of underlying structures could have localized Mesozoic Elmira Peak along the north edge of the map (too small magmatism and tectonism. to show on the map), has surface features interpreted as Riedel shears (Petit, 1987). Together these lines CRETACEOUS THRUST FAULTS of evidence suggest that there was late Cretaceous thrusting, at least north of the Hope fault.

South of the map, the Magee fault zone was attributed The Spokane dome mylonite zone in the Priest River to normal fault back sliding of a steepened eastward complex is arguably another Cretaceous structure. verging thrust system (Lewis and others, 2002). The Metamorphic monazite ages around 72 Ma from northern end of this zone is a transfer or transform the Hauser Lake gneiss (Ygs) on Hoodoo Mountain system that strikes west-northwest into the southern part (Doughty and others, 1998), and zircon overgrowth of the Sandpoint map at about 116° 15' west longitude. and titanite in a garnetiferous amphibolite, suggest The best candidate for the northern continuation of metamorphism about 70 Ma (Doughty and Chamberlain, the Magee fault zone is the very steep and overturned 2008). How much deformation accompanied Grenville strata west of Johnson Creek and the Packsaddle fault. age metamorphism, recorded by rims of detrital zircons Harrison and Jobin (1963, 1965) showed this fault in the Hauser Lake gneiss (Doughty and Chamberlain, along Johnson Creek projecting north-northeast to 2008), is unknown. The Spokane dome mylonite zone the Hope fault and apparently interpreted it as one of has been well documented to the south (e.g., Rhodes many “block faults” that accommodated block tilting. and Hyndman, 1984; Doughty and Price, 1999) but also However, its spatial association with anomalously steep extends north of the Pend Oreille River between the East

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Newport and Purcell Trench faults (Figure 50). Most EOCENE EXTENSIONAL FAULTS rocks in it are variously mylonitized with mylonitic lineations generally plunging shallowly to the east- northeast, some west-southwest. The mylonitic fabric There are two major sets of faults that probably generally dips to the north or northeast, although it accommodated extension during the Eocene, although appears folded about north-plunging axes. An exception they may have earlier histories. One set strikes generally is near Prater Mountain, where the folded fabric forms north-northeast, the other, northwest. The first set includes the Purcell Trench, East Newport, Twin Creek, the Prater Mountain antiform and dips south under and numerous unnamed faults. The set with northwest the Wrencoe pluton. This mylonitic fabric contains strikes includes the Hope, Pack River, Glad Creek, kinematic indicators that are consistently top-to-the Mirror Lake, and numerous unnamed faults. east, except near the East Newport fault, where tops- west motion is attributed to deformation younger than Cretaceous. The East Newport fault appears to truncate EAST NEWPORT FAULT the top of the mylonite zone north of Prater Mountain, although the top of the zone is poorly defined. Rocks in the eastern part of the Selkirk crest are in the footwall of the East Newport fault, a down-to-the-west The Spokane dome mylonite zone was initially mapped normal fault that dropped relatively low-grade Prichard by Cheney (1980), Rhodes and Hyndman (1984), and Formation to the west against high-grade orthogneiss Rehrig and others (1987), and later studied in more and paragneiss of the Priest River complex to the east detail by Doughty and Price (1999, 2000). There is (Harms and Price, 1992; Doughty and Price, 1999). disagreement about the relationship between the Spokane Most kinematic indicators near the East Newport fault dome mylonite zone and the Purcell Trench fault. Rehrig show tops-west motion. Westward younging of argon and others (1987) related the mylonite to a fault in the ages in the Selkirk crest toward the fault (Doughty and Purcell Trench (the Purcell-Coeur d’Alene detachment) Price, 2000) supports eastward tilting of the footwall and considered the entire Priest River complex a typical (rocks to the west would be uplifted and cooled through Cordilleran metamorphic core complex. Rhodes and their blocking temperatures later than those to the east). Hyndman (1984) pointed out that the lack of chlorite A strong possibility is that the Sandpoint conglomerate breccia at the top of the Spokane dome makes it (Tc) was deposited on the footwall of this fault from dissimilar to a classic metamorphic core complex sediment derived from the uplifted footwall east of and suggested that the mylonite is possibly the basal it before it was segmented, and its parts separated by décollement of the Sevier thrust belt. One candidate for displacement on the Purcell Trench fault and antiformal the basal décollement is the thrust fault that places pre- uplift of the Priest River complex (Doughty and Price, Belt augen gneiss (Yag) over meta-Belt (Ygs) southeast 2000). If so, a piece of the fault is buried under the of Priest River (see cross section B-B'). Doughty and conglomerate in the Purcell Trench. Based on ages Price (1999, 2000) showed the Purcell Trench fault of clasts in Tc, the fault was active after 51 Ma, and merging with the Spokane Dome mylonite at depth and perhaps before 47 Ma (Doughty and Price, 2000). attributed the arching of the mylonite zone to uplift of the The age of the southern part of the fault is bracketed footwall of the Purcell Trench fault after unroofing by by a 50 Ma age of a pluton to the west that cuts the the East Newport fault before final displacement on the Newport fault and is interpreted as late to synkinematic, and a 48 Ma age from the undeformed Wrencoe pluton Purcell Trench fault. In contrast, Rhodes and Hyndman (Stevens and others, 2015). Based on predominance of (1984) showed a shallow dipping Purcell Trench fault lower Prichard lithologies and fine-grained Eocene dike cutting the mylonite zone at a small angle. To the south rocks in the Sandpoint conglomerate that are similar in the Coeur d’Alene 30' x 60' quadrangle we showed a to dikes in Ypab to the east in the Cabinet range, most similar crosscutting relationship but with a steeper fault of the overlying Belt Supergroup and younger strata and larger intersection angle (Lewis and others, 2002). had already been eroded from the Selkirk crest by this We suspect that this is true in the Sandpoint area too, time. Deep erosion of an arch in the Belt strata west although perhaps with a smaller angle. Crosscutting of of the map is documented by Eocene volcanic and the mylonite zone by both the East Newport and Purcell volcaniclastic rocks unconformably overlying Prichard Trench faults indicates that it is older than they are and and progressively younger strata going from southeast plausibly Cretaceous. to northwest (Miller, 2000).

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PURCELL TRENCH FAULT 49 Ma biotite age from a granitic rock near the mouth of Tavern Creek (Miller and Engels, 1975; recalculated The Purcell Trench fault is not exposed within this map’s with present decay constants). Intermediate ages (56 Ma boundaries, but its existence is inferred from contrast on muscovite and 59 Ma on biotite) from the area of of metamorphic grade and deformation in bedrock moderate metamorphic grade (Ygq unit) near Colburn exposures across the Purcell Trench (Miller and others, suggest that those rocks are in the hanging wall of a 1999; Doughty and Price, 1999). The fault is inferred western splay of the fault (Doughty and Price, 2000). to dip moderately eastward with normal displacement, Location of the Purcell Trench fault north of the Pack although it may have started as a low-angle detachment River is uncertain because of less obvious contrast in that steepened during unroofing and doming of the Priest metamorphic grade. We place it east of where it was River complex or was later offset by a steeper normal mapped by Miller and others (1999) and continue it fault. Local mylonitic fabrics in the footwall west of farther north than Doughty and Price (1999, 2000), but Colburn and Elmira are presumed to be associated with about where Doughty and Price (2000) show sillimanite- the fault. Within 1,000 m (3,280 ft) of the valley there bearing rocks in contact with phyllite or schist that lack are steeply east-dipping mylonitic shear bands spaced aluminosilicate minerals. The metamorphosed Prichard at intervals of about 2 to 4 cm in the granitic rocks Formation (Ypmt) on Elmira peak is interpreted to be in (Doughty and Price, 2000). Kinematic indicators there the footwall of the fault, with the Sandpoint conglomerate show top-to-the-east shear trending 063º and plunging and relatively unmetamorphosed Prichard Formation 26º (Doughty and Price, 2000). Alternatively, these (Ypab) in the hanging wall. Ypmt contains coarse lenses mylonites could be the diffuse upper boundary to the of muscovite, interpreted as retrograded sillimanite Spokane dome mylonite zone. (Figure 46) and locally, garnet. On and southwest of Elmira Peak, two amphibolite samples yielded There are two matches across the fault that can be used metamorphic temperatures and pressures above 700°C as piercing points to estimate accommodated extension. and 6 kb, similar to those across the topographic trench One is correlating the trace of the East Newport fault (Doughty and Price, 2000). However, nearby muscovite with the east edge of the Sandpoint conglomerate. and biotite 40Ar/39Ar plateau ages of 67.6 Ma and 63.4 Current separation of about 28 km (17 mi) likely is a Ma, respectively, are intermediate between younger maximum estimate of horizontal displacement on the ages from the Priest River complex and older ages from fault because erosion to remove any Tertiary sediment east of the Purcell Trench fault; their discordance and from west of the Selkirk crest would have shifted the disturbed 40Ar/39Ar spectra were interpreted to result trace of the fault farther west. A magnetotelluric profile from slow cooling followed by quenching during from a line run about 20 km (12 mi) farther north was Eocene uplift (Doughty and Price, 2000). In contrast, a interpreted to show horizontal displacement of about 26 new 89.61 ± 0.74 40Ar/39Ar weighted plateau age from km (16 mi) (Bedrosian and Box, 2016). biotite (Figure 51) 3.4 km east of Elmira Peak is similar The fault section west of the Sandpoint conglomerate to ages from east of the fault. The contrast in these (Tc) could not have been active before about 49 Ma biotite ages seems too great to explain by tilting of a if its motion severed and separated the East Newport single block but is consistent with the Purcell Trench fault. History of motion elsewhere, especially north and fault being where mapped. The intermediate age and south of the Newport fault system, is based on contrast pressure from Elmira Peak suggest that there is a splay in cooling ages. Cretaceous granitic rocks east of the under or near Elmira. fault yield Cretaceous K-Ar ages (see Kpd, Kbgd, Khgd and Kt), but west of the fault yield Eocene cooling ages (Harrison and others, 1972; Miller and Engels, 1975), reflecting Eocene relative uplift of the west side (Doughty and Price, 1999). Biotite from the Kmg unit 2 km (1 mi) southwest of Colburn and west of the fault yielded a 48.7 ± 0.7 Ma 40Ar/39Ar plateau (Doughty and Price, 1999). Other young ages are 51 to 53 Ma from an 40Ar/39Ar age spectrum from biotite in a granitic dike northwest of Walsh Lake (Fillipone, 1993) and a

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200 Ar-Ages in Ma 190 180 WEIGHTED PLATEAU 06RL417 biotite 89.61 ± 0.74 170 TOTAL FUSION 93.59 ± 0.73 160 NORMAL ISOCHRON 150 87.60 ± 1.55 INVERSE ISOCHRON 140 85.10 ± 2.16 130 MSWD 120 2.20

Age (Ma) 89.61 ± 0.74 Ma 110 100

90 Sample Info 80 BIOTITE 70 P30 60 DF IRR = OS16 50 J = 0.0037820 ± 0 10 20 30 40 50 60 70 80 90 100 0.0000189

Cumulative 39Ar Released (%)

Figure 51. Biotite 40Ar/39Ar weighted plateau age from Prichard Formation (Yab) collected 3.4 km (2.1 mi) east of Elmira Peak (48.4917°N, 116.3843°W; NAD27). Analytical results from David Foster at the Department of Geological Sciences, University of Florida.

TWIN CREEK AND UNNAMED FAULTS are opposite rocks of and above the Wallace Formation, EAST OF THE PURCELL TRENCH yet nearer Sandpoint, rocks on either side of the Hope fault may be from equivalent stratigraphic levels low in the Prichard Formation. Displacement on the fault These faults generally strike parallel to the Purcell transfers both to the north into the Pack River fault and Trench fault, and they typically drop younger south into parallel, down-to-the-southwest faults such stratigraphic units down to the west. Interpretation that the east contact of the Sandpoint conglomerate northeast as the Mirror Lake fault. There also is a concentration of Sandpoint is such a fault (Doughty and Price, 2000) of Eocene dikes along and near the Hope fault near its supports an Eocene age. Most faulted strata also dip intersection with the Purcell Trench fault and the Eocene eastward, suggesting fault motion was either listric, or Wrencoe pluton. It seems likely that the Wrencoe pluton bookshelf-like with block tilt to the east. Both motions and related dikes intruded the fault during at least its appear antithetic to the Purcell Trench fault. last activity, which may have included motion west of the Purcell Trench fault. However, kinematic evidence only documents dip-slip movement, with the Hope fault HOPE FAULT acting in conjunction with the (southern) Purcell Trench fault during the Eocene (Fillipone and Yin, 1994; The Hope fault, its regional role, and its intersection Doughty and Price, 2000). Minor but important faults in with the Purcell Trench fault were discussed by this set include the Glad Creek fault near the northwest Harrison and others (1972), Fillipone and Yin (1994), corner of the map, and the Mirror Lake fault in the and Doughty and Price (2000). Although its straight south-center part of the map. Lineated dikes northwest trace is consistent with strike-slip motion, kinematic of Sandpoint that are unlike porphyries related to analysis only supports dip slip movement (Fillipone, the Wrencoe pluton may record extension there that 1993). Minimum dip slip based on thermochronometry predates intrusion of the Wrencoe. is 4 km (Fillipone and others, 1995). Stratigraphic offset across the Hope fault decreases northwestward from the east edge of the map toward Sandpoint. North of Clark Fork, Idaho, rocks of the middle Prichard (Ypf)

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PACK RIVER FAULT REFERENCES

The herein named Pack River fault extends southeast from near Colburn. Eocene Sandpoint conglomerate Anderson, A.L., 1947, Lead-silver deposits of the (Tc) and Prichard Formation (Ypab) are downfaulted Clark Fork district, Idaho: U.S. Geological Survey on its southwest side. Metasedimentary rocks on the Bulletin 944-B, 117 p. northeast side (Ygq) are higher in metamorphic grade Anderson, H.E., and Davis, D.W., 1995, U-Pb than Ypab south of the fault. geochronology of the Moyie sills, Purcell Supergroup, southeastern British Columbia: Implications for the Mesoproterozoic geological MIRROR LAKE FAULT history of the Purcell (Belt) basin: Canadian Journal of Earth Sciences, v. 32, no. 8, p. 1180-1193. A significant fault zone south of the Hope fault places Anderson, H.E, and Goodfellow, W.D., 2000, rocks of the Prichard Formation on the northeast against Geochemistry and isotope chemistry of the Moyie those of the Revett, St. Regis, Helena, and Wallace sills: Implications for the early tectonic setting formations on the southwest. We interpret this zone to of the Mesoproterozoic Purcell basin: in Lydon, comprise southwest-dipping normal faults with down- J.W. Höy, T., Slack, J.F., and Knapp, M.E., eds., to-the-southwest motion. This configuration could The Geological Environment of the Sullivan easily account for the sliver of Revett Formation near Deposit, British Columbia: Geological Association of Talache Landing as well as the tight syncline that of Canada, Mineral Deposits Division, Special repeats Ysr. Reverse-slip on a northeast dipping fault Publication No. 1, p. 302-321. could produce the same map pattern but the dip would have to be very steep in order to strand Revett between Anderson, D., and Höy, T., 2000, Fragmental the east-facing middle Belt rocks on the southwest and sedimentary rocks of the Aldridge Formation, complexly folded and faulted middle Prichard rocks on Purcell Supergroup, British Columbia: in Lydon, the northeast. A fault along Maiden Creek to the south J.W., Höy, T., Slack, J.F., and Knapp, M.E., eds., also appears to have been down to the south. Both The Geological Environment of the Sullivan probably connect with faults on the east side of the lake. Deposit, British Columbia,: Geological Association of Canada, Mineral Deposits Division, Special Publication No. 1, p. 259-271 ACKNOWLEDGMENTS Bedrosian, P.A., and Box, S.E., 2016, Highly conductive horizons in the Mesoproterozoic Belt-Purcell basin: Sulfidic early basin strata as key markers of David M. Miller, Fred K. Miller, and Stephen E. Box Cordilleran shortening and Eocene extension: in of the U.S. Geological Survey kindly provided field MacLean, J.S., and Sears, J.W., eds., Belt Basin: maps, thin sections, and geochemical results from the Window to Mesoproterozoic Earth: Geological Sandpoint region that were used extensively in the Society of America Special Paper 522, p. 305-339. compilation of the western half of the map. Numerous Bennett, E.H., II, Kopp, R.S., and Galbraith, J.H., 1975, discussions with P. Ted Doughty along with his mapping Reconnaissance geology and geochemistry of the assistance in 2003 greatly improved our understanding Mt. Pend Oreille quadrangle and surrounding areas: of the geology of the area. Don Winston and Brian White Idaho Bureau of Mines and Geology Pamphlet 163, shared their views on the Belt Supergroup on numerous 83 p., scale 1:62,500. occasions and strongly influenced our stratigraphic Bishop, D.T., 1973, Petrology and geochemistry of interpretations. Editorial work by Kate Schalck at the the Purcell sills in Boundary County, Idaho: Belt Idaho Geological Survey improved the manuscript Symposium, v. 2, Idaho Bureau of Mines and considerably. Use of accommodations at the University Geology Special Publication, p. 16-66. of Idaho Field Campus in Clark Fork and the USFS Bishop, D.T., 1976, Petrology and geochemistry of the Priest River Experimental Forest facilities is gratefully Purcell sills, Boundary County, Idaho and adjacent acknowledged as is permission to access private land. Mapping and compilation were supported by the U.S. areas: University of Idaho Ph.D. thesis, 147 p. Geological Survey STATEMAP program. Boleneus, D.E., Appelgate, L.M., Joseph, N.L., and Brandt, T.R., 2001, Raster images of geologic

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maps of Middle Proterozoic Belt strata in parts and Lewis, R.S., 2006a, Geologic map of the Derr of Benewah, Bonner, Kootenai and Shoshone Point quadrangle, Bonner and Shoshone counties, counties, Idaho, and Lincoln, Mineral and Sanders Idaho: Idaho Geological Survey Digital Web Map counties, Montana: U.S. Geological Survey Open- 59, scale 1:24,000. File Report 01B438, 35 p. Burmester, R.F., McFaddan, M.D., Breckenridge, R.M., Breckenridge, R.M., and Othberg, K.L., 1998, and Lewis, R.S., 2006b, Geologic map of the Chronology of glacial Lake Missoula floods: Talache quadrangle, Bonner County, Idaho: Idaho paleomagnetic evidence from Pleistocene lake Geological Survey Digital Web Map 75, scale sediments near Clark Fork, Idaho: Geological 1:24,000. Society of America Abstracts with Programs, v. 30, Burmester, R.F., Lewis, R.S. McFaddan, M.D., no. 6, p. 5. Breckenridge, R.M., Miller, D.M., and Miller, F.K., Breckenridge, R.M., and Phillips, W.M., 2010, New 2007, Geologic map of the Cocolalla quadrangle, cosmogenic 10Be surface exposure ages for the Bonner County, Idaho: Idaho Geological Survey Purcell Trench lobe of the Cordilleran ice sheet in Digital Web Map 91, scale 1:24,000. Idaho: Geologic Society of America Abstracts with Burmester, R.F., Breckenridge, R.M., Lewis, R.S., Programs, v. 42, no. 5, p. 309. and McFaddan, M.D., 2009, Geologic map of the Breckenridge, R.M., Burmester, R.F., Lewis, R.S., Moravia quadrangle, Boundary County, Idaho: and McFaddan, M.D., 2014, Geologic map of Idaho Geological Survey Digital Web Map 107, the east half of the Bonners Ferry 30 x 60 minute scale 1:24,000. quadrangle, Idaho and Montana: Idaho Geological Bush, J.H., 1989, The Cambrian system of northern Survey Digital Web Map 173, scale 1:75,000. Idaho and northwestern Montana: in Chamberlain, Brownfield, S.H., Nettleton, W.D., Weisel, C.J., V.E., Breckenridge, R.M., and Bonnichsen, B., Peterson, N., and McGrath, C., 2005, Tephra eds., Guidebook to the Geology of Northern and influence on Spokane-flood terraces, Bonner Western Idaho and Surrounding Area: Idaho County, Idaho: Soil Science Society of America Geological Survey Bulletin 28, p. 103-121. Journal, v. 69, p. 1422–1431. Chandler, F.W., 2000, The Belt-Purcell basin as a low- Burmester, R.F., 1986, Preliminary geologic map of the latitude passive rift: implications for the geological Leonia area, Idaho and Montana: U.S. Geological environment of Sullivan type deposits: in Lydon, Survey Open-File Report 86-554, 13 p., scale J.W., Höy, T., Slack, J.F., and Knapp, M.E., eds., 1:48,000. The Geological Environment of the Sullivan Burmester, R.F., and Lewis, R.S., 2011, A case for post- Deposit, British Columbia: Geological Association 100 Ma fault block tilting of a Cretaceous laccolith, of Canada, Mineral Deposits Division, Special Bonner County, Idaho: Northwest Geology, v. 40, Publication No. 1, p. 82-112. p. 27-36. Cheney, E.S., 1980, Kettle dome and related structures Burmester, R.F., Breckenridge, R.M., Lewis, R.S., and of northeastern Washington: in Crittenden, M.D., McFaddan, M.D., 2004a, Geologic map of the Jr., Coney, P.J., and Davis, G.H., eds., Cordilleran Clark Fork quadrangle, Bonner County, Idaho: Metamorphic Core Complexes: Geological Society Idaho Geological Survey Digital Web Map 25, of America Memoir 153, p. 463-483. scale 1:24,000. Clark, S.H.B., 1967, Structure and petrology of the Burmester, R.F., Breckenridge, R.M., Lewis, R.S., and Priest River-Hoodoo Valley area, Bonner County, McFaddan, M.D., 2004b, Geologic map of the Idaho: University of Idaho Ph.D. thesis, 137 p. Hope quadrangle, Bonner County, Idaho: Idaho Cressman, E.R., 1985, The Prichard Formation of the Geological Survey Digital Web Map 26, scale lower part of the Belt Supergroup, Proterozoic 1:24,000. Y, near Plains, Sanders County, Montana: U.S. Burmester, R.F., Breckenridge, R.M., Lewis, R.S., Geological Survey Bulletin 1553, 64 p. and McFaddan, M.D., 2004c, Geologic map of Cressman, E.R., 1989, Reconnaissance stratigraphy the Scotchman Peak quadrangle, Bonner County, of the Prichard Formation (Middle Proterozoic) Idaho: Idaho Geological Survey Digital Web Map and the early development of the Belt basin, 24, scale 1:24,000 Washington, Idaho, and Montana: U.S. Geological Burmester, R.F., Breckenridge, R.M., McFaddan, M.D. Survey Professional Paper 1490, 80 p.

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Cressman, E.R., and Harrison, J.E., 1986, Geologic map Evans, K.V., and Fischer, L.B., 1986, U-Th-Pb of the Yaak River area, Lincoln County, northwest geochronology two augen gneiss terranes, Idaho: Montana: U.S. Geological Survey Miscellaneous New data and tectonic implications: Canadian Field Studies Map MF-1881, scale 1:48:000. Journal of Earth Sciences, v. 23, p. 1919-1927. Doblas, M., 1998, Slickenside kinematic indicators: Evans, K.V., Aleinikoff, J.N., Obradovich, J.D., Tectonophysics, v. 295, p. 187–197. and Fanning, C.M., 2000, SHRIMP U-Pb Doughty, P.T., 1995, Tectonic evolution of the Priest geochronology of volcanic rocks, Belt Supergroup, River complex and the age of basement gneisses: western Montana; evidence for rapid deposition Constraints from geochronology and metamorphic of sedimentary strata: Canadian Journal of Earth thermobarometry: Queen’s University Ph.D. thesis, Sciences, v. 37, no. 9, p. 1287-1300. 408 p. Fillipone, J.A., 1993, Tectonic and thermochronologic Doughty, P.T., and Chamberlain, K.R., 2008, Protolith evolution of the Cabinet and Selkirk mountains, age and timing of Precambrian magmatic and northwest Montana and northeast Idaho: University metamorphic events in the Priest River complex, of California at Los Angeles Ph.D. thesis, 341 p. northern Rockies: Canadian Journal of Earth Fillipone, J.A., and Yin, An, 1994, Age and regional Sciences, v. 45, no. 1, p. 99-116. tectonic implications of Late Cretaceous thrusting Doughty, P.T., and Price, R.A., 1999, Tectonic evolution and Eocene extension, Cabinet Mountains, of the Priest River complex, northern Idaho and northwest Montana and northern Idaho: Geological Washington: A reappraisal of the Newport fault Society of America Bulletin, v. 106, p. 1017-1032. with new insights on metamorphic core complex Fillipone, J.A., Yin, A., Harrison, T.M., Gehrels, G., formation: Tectonics, v. 18, no. 3, p. 375-393. Smith, M., and Sample, J.C., 1995, Age and Doughty, P.T., and Price, R.A., 2000, Geology of magnitude of dip-slip faulting deduced from the Purcell Trench rift valley and Sandpoint differential cooling histories: an example from the conglomerate: Eocene en echelon normal faulting Hope fault, northwest Montana: The Journal of and synrift sedimentation along the eastern flank Geology, v. 103, no. 2, p. 199-211. of the Priest River metamorphic complex, northern Finch, J.C., and Baldwin, D.O., 1984, Stratigraphy of Idaho: Geological Society of America Bulletin, v. the Prichard Formation, Belt Supergroup, in Hobbs, 112, no. 9, p. 1356-1374. S.W., ed., The Belt, Abstracts with Summaries, Belt Doughty, P.T., Price, R.A., and Parrish, R.R., 1998, Symposium II, 1983: Montana Bureau of Mines Geology and U-Pb geochronology of Archean and Geology Special Publication 90, p. 5-7. basement and Proterozoic cover in the Priest Gardner, D.W., 2008, Sedimentology, stratigraphy, River complex, northwestern United States, and and provenance of the upper Purcell Supergroup, their implications for Cordilleran structure and southeastern British Columbia, Canada: Precambrian continent reconstructions: Canadian Implications for syn-depositional tectonism, basin Journal of Earth Sciences, v. 35, p. 39-54. models, and paleogeographic reconstructions, Doughty, P.T., Buddington, A.M., Cheney, E.S., and University of Victoria, BC, thesis, 76 p. Derkey, R.E., 2016, Geology of the Priest River Garlick, W.G., 1988, Algal mats, load structures, and metamorphic complex and adjacent Paleozoic synsedimentary sulfides in Revett quartzite beds of strata south of the Spokane River Valley, Montana and Idaho: Economic Geology, v. 83, p. Washington, in Cheney, E.S., ed., The Geology of 1259-1278. Washington and Beyond: Laurentia to Cascadia: Glazner, A.F., Bartley, J.M., Coleman, D.S., Gray, W., Seattle, University of Washington Press, p. 77-92. and Taylor, R.Z., 2004, Are plutons assembled Etienne, J.E., 1987, Geology and mineral resources over millions of years by amalgamation from small of the Lightning Mountain-Rattle Creek area, magma chambers?: GSA Today, v. 14, no. 4/5, p. eastern Bonner County, Idaho: Eastern Washington 4-11. University M.S. thesis, 116 p. Gorton, M.P., Schandl, E.S., and Höy, T., 2000, Etienne, J.E., 1988, Geologic map and sections of the Mineralogy and geochemistry of the Middle Lightning Mountain-Rattle Creek area, eastern Proterozoic Moyie sills in southeastern British Bonner County, Idaho: Idaho Geological Survey Columbia: in Lydon, J.W., Höy, T., Slack, J.F., and Technical Report 88-1, scale 24,000. Knapp, M.E., eds., The Geological Environment of

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the Sullivan Deposit, British Columbia: Geological Hayes, T.S., 1983, Geologic studies on the genesis of Association of Canada, Mineral Deposits Division, the Spar Lake strata-bound copper-silver deposit, Special Publication No. 1, p. 322-335. Lincoln County, Montana: Ph.D. Dissertation, Green, W. R., 1976, Geology and mineral resources Stanford University, 340 p. of the Blacktail Mountain area, Bonner County, Hayes, T.S., and Einaudi, M.T., 1986, Genesis of the Spar Idaho: University of Idaho M.S. thesis, 108 p. Lake strata-bound copper-silver deposit, Montana: Harms, T. A., 1982, The Newport fault: Low-angle Part I, Controls inherited from sedimentation and normal faulting and Eocene extension, northeast preore diagenesis: Economic Geology, v. 81, p. Washington and northwest Idaho: Queens's 1899-1931. University M.S. thesis, 157 p Hoffer, M.R., 2005, Petrology and geochemistry of Harms, T.A., and Price, R.A., 1992, The Newport fault: Cretaceous plutons in the Careywood quadrangle, Eocene listric normal faulting, mylonitization, northern Idaho: University of Idaho M.S. thesis, 83 and crustal extension in northeast Washington and p. northwest Idaho: Geological Society of America Höy, T., Anderson, D., Turner, R.J.W., and Leitch, Bulletin, v. 104, p. 745-761. C.H.B., 2000, Tectonic, magmatic and metallogenic Harrison, J.E., 1969, Geologic map of part of the Mount history of the early synrift phase of the Purcell Pend Oreille quadrangle, Idaho-Montana: U.S. basin, southeastern British Columbia, in Lydon, Geological Survey Open-File Report 69-120, scale J.W., Höy, T., Slack, J.F., and Knapp, M.E., eds., 1:48,000. The Geological Environment of the Sullivan Harrison, J.E., and Jobin, D.A., 1963, Geology of the Deposit, British Columbia: Geological Association Clark Fork quadrangle, Idaho-Montana: U.S. of Canada, Mineral Deposits Division, Special Geological Survey Bulletin 1141-K, 38 p., scale Publication No. 1, p. 33-60. 1:62,500. Kidder, D.L., 1987, Stratigraphy, micropaleontology, Harrison, J.E., and Jobin, D.A., 1965, Geologic map of petrology, carbonate geochemistry, and depositional the Packsaddle Mountain quadrangle, Idaho: U.S. history of the Proterozoic Libby Formation, Geological Survey Geological Quadrangle Map northwestern Montana and northeastern Idaho: GQ-375, scale 1:62,500. U.S. Geological Survey Open-File Report 87-636, Harrison, J.E., and Schmidt, P.W., 1971, Geologic map 133 p. of the Elmira quadrangle, Bonner County, Idaho: Kleinkopf, M.D., Harrison, J.E., and Zartman, R.E., U.S. Geological Survey Geological Quadrangle 1972, Aeromagnetic and geologic map of part of Map GQ-953, scale 1:62,500. northwestern Montana and northern Idaho: U.S. Harrison, J.E., Kleinkopf, M.D., and Obradovich, J.D., Geological Survey Geophysical Investigations 1972, Tectonic events at the intersection between Map GP-830, scale 1:250,000. the Hope fault and the Purcell trench, northern Lane, E.W., 1947, Report of the subcommittee on Idaho: U.S. Geological Survey Professional Paper sediment terminology: Transactions of the 719, 24 p. American Geophysical Union, v. 28, no. 6, p. 936- Harrison, J.E., Kleinkopf, M.D., and Wells, J.D., 1980, 938. Phanerozoic thrusting in Proterozoic Belt rocks, Lemoine, S.R., and Winston, D., 1986, Correlation of northwestern Montana: Geology, v. 8, no. 9, p. 407- the Snowslip and Shepard formations of the Cabinet 411. Mountains with upper Wallace rocks of the Coeur Harrison, J.E., Griggs, A.B., and Wells, J.D., 1986, d’Alene Mountains, western Montana: in Roberts, Geologic and structure maps of the Wallace 1°x2° S.M., ed., Belt Supergroup: A Guide to Proterozoic quadrangle, Montana and Idaho: U.S. Geological Rocks of Western Montana and Adjacent Areas: Survey Miscellaneous Investigations Series Map Montana Bureau of Mines and Geology Special I-1509-A, scale 1:250,000. Publication 94, p. 161-168. Harrison, J.E., Cressman, E.R., and Whipple, J.W., Lewis, R.S., Burmester, R.F., McFaddan, M.D., 1992, Geologic and structural maps of the Kalispell Eversmeyer, B.A., Wallace, C.A., and Bennett, 1°x2° quadrangle, Montana, and Alberta and British E.H., 1992, Geologic map of the upper North Fork Columbia: U.S. Geological Survey Miscellaneous of the Clearwater River drainage, northern Idaho: Investigations Series Map I-2267, scale 1:250,000. Idaho Geological Survey Geologic Map Series, GM-20, scale 1:100,000,

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Lewis, R.S., Burmester, R.F., McFaddan, M.D., Derkey, Lewis, R.S., Vervoort, J.D., Burmester, R.F., and P.D., and Oblad, J.R.,1999, Digital geologic map Oswald, P.J., 2010, Detrital zircon analysis of the Wallace 1:100,000 quadrangle, Idaho, U.S. of Mesoproterozoic and Neoproterozoic Geological Survey Open-File Report 99-390, scale metasedimentary rocks of north-central Idaho: 1:100,000. implications for development of the Belt-Purcell Lewis, R.S., Burmester, R.F., Kauffman, J.D., and Frost, basin: Canadian Journal of Earth Sciences, v. 47, T.P., 2000, Geologic map of the St. Maries 30 x p. 1383-1404. 60 minute quadrangle, Idaho: Idaho Geological McFaddan, M.D., Breckenridge, R.M., Burmester, R.F., Survey Geologic Map 28, scale 1:100,000. and Lewis, R.S., 2006, Geologic map of the Cabinet Lewis, R.S., Burmester, R.F., Breckenridge, R.M., quadrangle, Bonner and Shoshone counties, Idaho: McFaddan, M.D., and. Kauffman, J.D, 2002, Idaho Geologic Survey Digital Web Map 60, scale Geologic map of the Coeur d’Alene 30 x 60 minute 1:24,000. quadrangle, Idaho: Idaho Geological Survey McKee, E.D., and Weir, G.W., 1963, Terminology for Geologic Map 33, scale 1:100,000. stratification and cross-stratification in sedimentary Lewis, R.S., Breckenridge, R.M., McFaddan, M.D., and rocks: Geological Society of America Bulletin, v. Burmester, R.F., 2006a, Geologic map of the Trout 64, p. 381-390. Peak quadrangle, Bonner County, Idaho: Idaho Meyer, S.E., 1999, Depositional history of pre-late and Geological Survey Digital Web Map 58, Scale late Wisconsin outburst flood deposits in northern 1:24,000. Washington and Idaho: An analysis of flood paths Lewis, R.S., Burmester, R.F., Breckenridge, R.M., and provenance: Washington State University M.S. Box, S.E., and McFaddan, M.D., 2006b, Geologic thesis, 91 p. map of the Sandpoint quadrangle, Bonner County, Miller, F.K., 1974, Preliminary geologic map of the Idaho: Idaho Geologic Survey Digital Web Map 76, Newport number 4 quadrangle, Pend Oreille, scale 1:24,000. Stevens, and Spokane counties, Washington: Lewis, R.S., Burmester, R.F. Breckenridge, R.M., Washington Division of Geology and Earth Resources Geologic Map GM-10, 6 p., scale McFaddan, M.D., Miller, F.K., and Miller, D.M., 1:62,500. 2006c, Geologic map of the Sagle quadrangle, Miller, F.K., 1982, Preliminary geologic map of the Bonner County, Idaho: Idaho Geologic Survey Coolin area: U.S. Geological Survey Open-File Digital Web Map 74, scale 1:24,000. Report 82-1061, scale 1:48,000. Lewis, R.S., Box, S.E. Breckenridge, R.M. Burmester, Miller, F.K., 2000, Geologic map of the Chewelah 30' R.F. and McFaddan, M.D., 2007a, Geologic map x 60' quadrangle, Washington and Idaho: U.S. of the Colburn quadrangle, Bonner County, Idaho: Geological Survey Miscellaneous Field Studies Idaho Geologic Survey Digital Web Map 89, scale Map MF-2354, scale 1:100,000. 1:24,000. Miller, F.K., and Burmester, R.F., 2004, Geologic map Lewis, R.S., Burmester, R.F., and Breckenridge, R.M., of the Bonners Ferry 30' x 60' quadrangle, Idaho and 2007b, Geologic map of the Elmira quadrangle, Montana: U.S. Geological Survey Miscellaneous Bonner County, Idaho: Idaho Geologic Survey Field Studies Map MF-2426, scale 1:100,000. Digital Web Map 90, scale 1:24,000. Miller, F.K., and Engels, J.C., 1975, Distribution and Lewis, R.S., McFaddan, M.D., Breckenridge, R.M., trends of discordant ages of the plutonic rocks and Burmester, R.F., 2007c, Geologic map of the of northeastern Washington and northern Idaho: Oden Bay quadrangle, Bonner County, Idaho: Geological Society of America Bulletin, v. 86, p. Idaho Geologic Survey Digital Web Map 88, scale 517-528. 1:24,000. Miller, F.K., Burmester, R.F., Powell, R.E., Miller, Lewis, R.S., Burmester, R.F., Breckenridge, R.M., D.M, and Derkey, P.D., 1999, Digital geologic McFaddan, M.D., and Phillips, W.M., 2008, map of the Sandpoint 1- by 2-degree quadrangle, Preliminary geologic map of the Sandpoint 30 x Washington, Idaho, and Montana: U.S. Geological 60 minute quadrangle, Idaho and Montana, and Survey Open-File Report 99-0144. the Idaho part of the Chewelah 30 x 60 minute Nelson, W.H., and Dobell, J.P., 1961, Geology of the quadrangle: Idaho Geological Survey Digital Web Bonner quadrangle, Montana: U.S. Geological Map 94, scale 1:100,000. Survey Bulletin 111-F, p. 189-235.

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Petit, J.P., 1987, Criteria for the sense of movement on Geological Society of America Special Paper 433, p. fault surfaces in brittle rocks: Journal of Structural 147-166. Geology, v. 9, p. 597–608. Sears, J.W., Chamberlain, K.R., and Buckley, S.N., 1998, Poage, M.A., Hyndman, D.W., and Sears, J.W., 2000, Structural and U-Pb geochronological evidence for Petrology, geochemistry, and diabase-granophyre 1.47 Ga rifting in the Belt basin, western Montana: relations of a thick basaltic sill emplaced into wet Canadian Journal of Earth Sciences, v. 35, p. 467- sediments, western Montana: Canadian Journal of 475. Earth Sciences, v. 37, no. 8, p. 1109–1119. Simpson, C., and Schmid, S.M., 1983, An evaluation of Redfield, T.F., 1986, Structural geology of part of the criteria to deduce the sense of movement in sheared Leonia quadrangle in northeast Idaho: Western rocks: Geological Society of America Bulletin, v. 94, Washington University M.S. thesis, 156 p. p. 1281-1288. Rehrig, W.A., Reynolds, S.J., and Armstrong, R.L., Stevens, L.M., Baldwin, J.A., Cottle, J.M., and Kylander- 1987, A tectonic and geochronologic overview of Clark, A.R.C., 2015, Phase equilibria modelling and the Priest River crystalline complex, northeastern LASS monazite petrochronology: P–T–t constraints Washington and northern Idaho, in Schuster, J.E., on the evolution of the Priest River core complex, ed., Selected Papers on the Geology of Washington: northern Idaho: Journal of Metamorphic Geology, Washington Division of Geology and Earth v. 33, p. 385–411. Resources Bulletin 77, p. 1-14. Stevens, L.M., Baldwin, J.A., Crowley, J.L., Fisher, C.M., Retallack, G.J., Sheldon, N.D., Cogoini, M., and Elmore, and Vervoort, J.D., 2016, Magmatism as a response R.D., 2003, Magnetic susceptibility of early Paleozoic to exhumation of the Priest River complex, and Precambrian paleosols: Palaeogeography, northern Idaho: Constraints from zircon U-Pb Palaeoclimatology, Palaeoecology, v. 198, p. 373- geochronology and Hf isotopes, Lithos, v. 262, p. 380. 285-297. Rhodes, B.P., and Hyndman, D.W., 1984, Kinematics Streckeisen, A.L., 1976, To each plutonic rock its proper of mylonites in the Priest River "metamorphic name: Earth-Science Reviews, v. 12, p. 1-33. core complex," northern Idaho and northeastern Weis, P.L., 1968, Geologic map of the Greenacres Washington: Canadian Journal of Earth Sciences, v. quadrangle, Washington and Idaho: U.S. Geological 21, no. 10, p. 1161-1170. Survey Geologic Quadrangle Map GQ-734, scale Rogers, C., Mackinder, A., Ernst, R.E., Cousens, B., 1:62,500. 2016. Mafic magmatism in the Belt-Purcell basin Weisel, C.J., Hartwig, P.M., Keirn, S.D., and Turner, and Wyoming Province of western Laurentia: B.J., 1982, Soil survey of Bonner County area, Belt Basin. in MacLean, J.S., and Sears, J.W., eds. Idaho, parts of Bonner and Boundary counties: Window to Mesoproterozoic Earth: Geological U.S. Department of Agriculture Soil Conservation Society of America Special Paper 522, p. 243-282. Service, 201 p. Ross, G.M., Parrish, R.R., and Winston, D., 1992, Weisenborn, A.E., and Weis, P.L, 1976, Geologic Provenance and U–Pb geochronology of the map of the Mount Spokane quadrangle, Spokane Mesoproterozoic Belt Supergroup (northwestern County, Washington, and Kootenai and Bonner United States): implications for age of deposition counties, Idaho: U.S. Geological Survey Geologic and pre-Panthalassa plate reconstructions: Earth Quadrangle Map GQ-1336, scale 1:62,500. and Planetary Science Letters, v. 113, no.1–2, p. Wentworth, C.K., 1922, A scale of grade class terms for 57–76. clastic sediments: Journal of Geology, v. 30, no. 5, Ross, G.M., and Villeneuve, M., 2003, Provenance of p. 377-392. the Mesoproterozoic (1.45 Ga) Belt Basin (western Whitehouse, M.J., Stacey, J.S., and Miller, F.K., 1992, North America): Another piece in the pre-Rodinia Age and nature of the basement in northeastern paleogeographic puzzle: Geological Society of Washington and northern Idaho: Isotopic evidence America Bulletin, v. 115, no. 10, p. 1191-1217. from Mesozoic and Cenozoic granitoids: Journal of Sears, J.W., 2007, Belt-Purcell Basin: keystone of the Geology, v. 100, p. 691-701. Rocky Mountain fold-and-thrust belt, United Winston, D., 1986, Sedimentology of the Ravalli States and Canada, in Sears, J.W., Harms, T.A., Group, middle Belt carbonate, and Missoula and Evenchick, C.A., eds., Whence the Mountains: Group, Middle Proterozoic Belt Supergroup,

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Montana, Idaho and Washington: in Roberts, S.M., ed., Belt Supergroup: A Guide to Proterozoic Rocks of Western Montana and Adjacent Areas: Montana Bureau of Mines and Geology Special Publication 94, p. 85-124. Winston, D., 1991, Evidence for intracratonic, fluvial, and lacustrine settings of Middle to Late Proterozoic basins of western U.S.A., in Gower, C.F., Rivers, T., and Ryan, B., eds., Mid-Proterozoic Laurentia- Baltica: Geological Association of Canada Special Paper 38, p. 535-564. Winston, D., 2007, Revised stratigraphy and depositional history of the Helena and Wallace formations, mid-Proterozoic Piegan Group, Belt Supergroup, Montana and Idaho: in Link, P.K., and Lewis, R.S., eds., Proterozoic Geology of Western North America and Siberia: SEPM (Society for Sedimentary Geology) Special Publication no. 86, p. 65-100. W Zirakparvar, N.A., Vervoort, J.D., McClelland, W., and Lewis, R.S., 2010, Insights into the metamorphic evolution of the Belt-Purcell basin; evidence from Lu-Hf garnet geochronology: Canadian Journal of Earth Sciences, v. 47, no. 2, p. 161-179.