Field Guide (With Road Logs) to Selected Parts of the Western and Central San Francisco Volcanic Field Coconino County, Arizona
FIELD GUIDE (WITH ROAD LOGS) TO SELECTED PARTS OF THE WESTERN AND CENTRAL SAN FRANCISCO VOLCANIC FIELD COCONINO COUNTY, ARIZONA The Arizona Geological Society Fall Field Trip September 24-26, 1982 by G. E. Ulrich, U.S. Geological Survey and R. F. Holm, Northern Arizona University I to Grand Canyon to Cameron ; ·, \ Firat dey route ,--:~~:.~~Q). I ROUTE 18 6 7 , Second day route I . ' ,, ' ' .2 Road log atop I \ I -, O'Leary / l Pea lc I /-----"'I l \ I .6 I I \ I / ,-r-" .._ 1 ¢J ,~ \ ,) ,"' "" ,..- ~-... ou -·r;--,"---"" ", \ ,, : San Franchco \ : Mountain 5~ \ u·•• T \\t~ ....... <••••• ( ','II' ) Pitman \ ·~ WilliaM• 1/"""\,----- ( ------"'~Parks- J 1:::•• I -"""- \.:'o\ __ .._•..•. ..,. 1·40 ''"--- ' ~ :; I\ · ----....._ I \ ~-• \\ ...... ' ~0 ~~ { ...... , "''"'\". \ "'....... '~. \I ' ~ ~~ ~,' ,_ \ ,~ '· _,,--...,. ( - ..... ' ......... ,.' I ---1 \ '--' ,...- - ' ------~--,-II --- .... I,- 2 \ \ I 1-17 0 SMI '- ... I I I I I I -.... 0 S 10 KM 1 I I II I I I Yotunleer Canyon ------------ ------- ------- ----------- - - Figure 1 Map of the central and western San Francisco volcanic field showing field-trip routes ··-- ··· -- · 0------ --- ------------------ ·- -- ~ INTRODUCTioNlf The San Francisco volcanic field is one of several late Cenozoic, basalt rich volcanic fields distributed around the southern marg in of the Colorado Plateau. In the San Francisco field, more than 600 vents, basaltic to rhyolitic in composition, have erupted through the Precambrian basement and a kilometer of nearly horizontal sedimentary rocks. Together with thei~ related flows and pyroclastic deposits, the mapped volcanic rocks cover approximately 2000 mi2 of the erosionally stripped surface of the Colorado Plateau in northern Arizona. The field is loosely defined as an area of volcanic deposits generally younger and more varied in composition than the basaltic series typically burying the .
[Show full text]