Series I B> DescriPtive Geology- 4l Bulletin No. 235 \ D, Petrography and Mineralogy, DEPARTMENT'OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY CHARLES \). WALCOTT, Di HECTOR GEOLOGICAL RECONNAISSANCE ACROSS THE CASCADE RANGE NEAR THE FORTY-NINTH PARALLEL GEORGE OTIS SMITH AND FRANK C. CALKINS WASHINGTON GOVERNMENT PRINTING OFFICE 1904 Trri-o^) SL'BD C 0 N T E N T S. I'lliJO. Letter of transmittal. ---_--_---..-.._-_.____.._-______._....._.._____.._.. 9 Introduction-__-._.__,.__-.----._--._._.__..._....__....---_--__._.__.-.-_- 11 Scope of report ---.--_.____.._______-.--....._---.._...._.__ ._.- 11 Route followed ........................:......................... 12 Geography .............................................................. 12 Topography .......................................................... 12 Primary divisions of the region..--.........-.--.-.--.-.-.. 12 Okanogan Valley .................:.. ............................ 18 Cascade Range ...............:........,..._ ....^......i........ 13 General characteristics..._.....-.....-..----.--.----.-.-..-.. 13 Northern termination.,.---.....-......--.-.............._ 13 Subdivision .............................................. 14 Okanogan Mountains ........................................... 14 Hozonieen Range ............................................ 15 Skagit Mountains....-.... ......-.----....-.-----..-...--.--- 16 Drainage ..................................................... 17 Climate ...................................................... ...... 17 Roads and trails -.-------.---..-.-..-.-.-..-..--.-..---.....-.--...---- 19 ............................................................... 20 Description of formations ...--..............-.-....--.-------.-.--... 20 Classification and mode of treatment .......-.-.---....-.---.. 20 Pre-Cretaceous rocks................------.-.-.--.--.--....---... 21 General character and distribution ..... , ..................... 21 Columbia and lower Okanogan valleys........................ 21 Upper Okanogan Valley ..._.........---.-.--. ................. 22 Basin of upper Skagit River.. ................................ 28 Lower Skagit Valley --...-----.-.------.....-----.-.-.-...---- 24 Mount Baker district ................................... ..... 25 Preliminary statement ..............................'..... 25 Supposed Paleozoic rocks ..-....-----.-----..----.---....- 26 Supposed Mesozoic rocks ............_..-.-.-.-......--... 27 Volcanics near Hannegan Pass ..........-. .---...--...... 27 Cretaceous strata ................................................. 28 Pasayten formation ............\................. ........ .... 28 Occurrence............................................... 28 Name ................,..'................................: 29 Lithologic character and thickness ....._-.-.'-.--.--...... 29 Tertiary formations.-----..-.-.....--...-..-..-..-.--------------.. 30 Classification and distribution.............-..-.-...-..----.-. 30 Columbia River Valley. ........................................ 30 Swauk formation ...............-..........--.----.----..-- 30 Andesite and rhyolite ..^................................. 31 Yakima basalt.....'........................-.---.--.----. 31 3 4 CONTENTS. ' Geology Continued. Page. Description of formations Continued. Tertiary formations Continued. Okanogan Valley ..--.....-.-..-.----.-.-.-. ..----.--...--.-- 32 Volcanics east of Hidden Lakes.-.----_--..------------------. 33 Western slope ..............1..........:...................... 34 Hamilton district............................ .."..... .. .--.. 34 Nooksak Valley..... -.-.....---.......-I................ 34 Quaternary formations.--......--....--....-.-. ..--.-----..----.. 34 Classification and distribution,............................... 34 Mount Baker lava ............................................ 35 Geologic relations .....'.-.-..--..............--..-...-..'-. 35 Lithologic characteristics .... ---..--..-.... ............ 35 Glacial and stream deposits --..------..-...-_.......-...-..-. 35 Columbia and Okanogan valleys.......................... 35 Mountain area _.................'.......................... 41 Western area __....._....__..._____.!.^_................I. 42 Intrusive rocks _-.-....--...----...--.--......---.....-.......... 43 Preliminary statement.....--...-----...-.................... 43 General classification.........- -.-.......-....---.......... 43 Method of treatment ...'............ ...................,.... 44 . Along the Columbia.......................................... 44 Megascopic features of granodiorite L...-.-................ 44 Occurrences of.granodiorite...---... -.-.-................ 45 Okanogan Valley..'........................................... 45 Granitic and dioritic rocks ............................... 45 Gabbro and diabase near Loomis ............-.---....--.. 46 Okanogan Mountains.....-.......-.--.....-.....-..-...--.-.. 47 Ultrabasic intrusives of Mount Chopaka.................. .47 Composite character of the granite belt_.................. 47 Biotite-granite ..-....--...-. 1 -.-.'.--............... 1..... 47 Granodiorite-.-....-...--..-...-.-.--...-....-----....--- 47 Diorite of the Horseshoe.................................. 48 Biotite-muscovite-granite ................................ 48 Hozomeen Range -..---.--.--..--.--.......-.......--...---... 49 Quartz-diorite.. ........--..-.-------...-.-- ------........ 49 Serpentine (saxonite) ...-...--.-----.--------------------- 49 Dike rocks-.-.....-........-.....-----....-.........-..... 49 . Skagit Valley and Skagit Mountains.. ...... ^.................. 49 Eastern portion.......................................... 49 Western portion -....-.--...........'.................'...,. 50 Petrography ................................................^........ 51 Introductory statement. ............^...................... ...... 51 Metamorphic rocks ...--....-.---.-.-..........--.-.---......--.-. 52 Altered basic lava near Loomis_....--.............---.-.-.-.. 52 Schists of Skagit Valley ...................................... 53 Chloritic schists.- __.__.'-_______-..__.-.-.._____-__"..__--. 53 Glaucophane-schists. - ..........^......................... 53 Volcanic rocks .;.',-.--....-;'-.--....-.._.. ...--.-..- ...---...---- 54 Distribiition and classification .............."..........-.-..... 54 Rhyolites -.....-.--.----------....----_-..--...----.-.-..-.-.- 55 Soda-rhyolite near Wenatchee...............:..-..-...... 55 Soda-rhyolite near Clover ...'.,....... r .^.......,....,..... 56 CONTENTS. 5 Geology Continued. Pl^e- Petrography Continued. Volcanic rocks Contimied. Andesites.....-..--.-...;--..--.....-...-...--.----.----.--.-. 56 Dacite.._..____.--.-._-___-----_..-----.-.--------..------ 56 Hornblende-pyroxeue-andesite...._---.-_-.--..-----.--.--- 56 Pyroxene-andesite of Mount Baker .......1............... 57 Basaltic augite-andesite .....--.-..-........----....-.-.-. 59 Pyroxene-andesites of Skagit Valley and Sank Mountain .. 60 Basalts,..........-.-.-..-...-..-................-."------------ 60 Hypersthene-basalt .--.-.--.....-----'...-:.----.--.--.--. 60 Yakima basalt -___....__..._ ..___..____.._... ...--..--..-.- 60 Metabasalts. _._.._._. _._..___.___._.._.__..---.---- .---.. 61. Plutonic rocks..-..-...-.--.-.-..---..----..._.....--..----...-.-. 61 Distribution and classification ______._.________.__--._---..---. 61 Granites.......................... ...................... .. ...... 62 Biotite-muscovite-granite of Mount Renimel type......... 62 Classificatory position.........................-.-..:..... 68 Biotite-muscovite-granite of Okanogan Valley type........ 68 Biotite-granite ............_..........._.... r _............. 65 Granodiorites-................................................ '66 Acidic granodiorite of Mount Baker district .............. 66 Basic type of granodiorite ................. .^............ 67 Diorites ............................................. .....^... 69 Quartz-mica-diorites---------_--------.-.----.--..- ------ 69 Quartz-pyroxene-mica-diorite ..........._.......---_....... 70 Quartz-augite-mica-diorite'..-.-.----..-.------..-.--...-. 70 Gabbros ..-.--...-..-..-- .......-.-.-...-......--....-. ...... 71 Olivine-hornblende-gabbro ..................-..-....._... 71 Uralitic gabbro of Palmer Mountain -.....-...---.'........ 72 Uralitic gabbro of Mount Chopaka ... ...'................ 72 Ultrabasic rocks .^............................................ 73 Serpentines and pyroxenites of Mount Chopaka ........... 73 Saxonite of Ruby Creek .____...__..._..__...--_.,-..___._. 73 Hypabyssal rocks. .................................................. 73 Classification and distribution.........--.-....-..-.-.--...... 78 Acidic dike rocks --.-----.-..----.-.--..-..........--........ 74 Granophyre ............................................... 74 Granite-porphyries ..... ...........'...................... 75 Pegmatites ........................... ....-'............. 75 Aplites ... ......-.----.--...---.-..-..-.--..--.-.-..--..-.. 76 '' Soda-syenite ".......................................... 76 Lamprophyric dike rocks -...-.-..---..--...... -..--......... 76 General characteristics. ......:........^................... 76 Diorite-porphyries .............'...........-.............. 77 Hornblende-porphyries................................... 77 Diorite (?) of Granite Mountain ........................... 78 Diabases........------.-----.-.-....- _._._-_:.._._______. .79 Peridotite ................................................