GEOLOGIC MAPS AND NOTES ALONG HIGHWAY 49 



By OLIVER E. BOWEN Jit. and RICHARD A. CBIPPEN JR. 



OUTLINE OF REPORT 



Page 



Introduction 35 



Mariposa to Coulterville Map 1 35 



Coulterville to Chinese Camp .Map 2 47 



Chinese Camp to Altaville Map 3 48 



Altaville to Mokelumne Hill Map 4 56 



Mokelumne Hill to Plymouth Map 5 62 



Plymouth to Placerville Map 6 65 



Placerville to Auburn Map 7 68 



Auburn to Xorth San Juan Map 8 73 



Xorth San Juan to Downieville Map 9 78 



Downieville to Sattley Map 10 84 



Introduction 



California State Highway 49, variously known as the Mother Lode 

 Highway or the Golden Highway, traverses 277 miles of the Sierra 

 Nevada, beginning at Mariposa on the south and ending at Sattley on the 

 north. It passes through nine comities, each of which represents an 

 important part of the Sierran Gold Belt. 



This entire region has come to be known generally as the Mother 

 Lode Country, but more technically speaking, the Mother Lode is a belt 

 of gold-bearing quartz veins which appears to start at Mariposa and to 

 terminate at Georgetown in Placer County. It forms a more or less con- 

 tinuous belt of quartz veins that occupy a fault zone approximately one 

 mile wide and 120 airline miles long. The 10-mile segment of this belt 

 between Jackson and Plymouth is its richest section and was the source of 

 one-half the gold produced in the entire 120-mile extent, which has 

 amounted to a quarter of a billion dollars. It is noteworthy that this 10- 

 mile segment lies at the bend in the belt where its trend changes from 

 northwest to nearly due north. The fault structure with which the Mother 

 Lode quartz veins are associated may possibly extend 50 miles farther 

 northward to Downieville, but Highway 49 leaves the Mother Lode at 

 Placerville and swings 10 or 15 miles to the west, traversing the even more 

 productive Grass Valley-Nevada City district and other gold-bearing 

 areas of the northern Sierra Nevada. 



The veins range from great white quartz masses 150 feet wide, down 

 to stringers less than the thickness of one 's little finger. The thickness of 

 a vein is no criterion as to its potential value. Rich pocket mines such as 

 those of Jackass Hill were found largely in narrow veinlets, whereas the 

 massive silica-carbonate rock of the Penon Blanco is practically barren 

 of gold. 



Mining methods and techniques developed in the California gold belt 

 have spread to the far corners of the earth and have become standard 

 practice everywhere. Many famous technicians and financiers had their 

 training in the Mother Lode Country before attaining even greater dis- 

 tinction and achievement in other fields. Bret Harte and Mark Twain owe 



much of their reputation to the gold country, and through their stories 

 the romance of the region has become familiar to all the world. 



Although so much has been written of the history, romance, and 

 folklore of the Sierran Gold Belt, little of general geologic interest has 

 been published for the use of the traveler. The following notes on geology 

 along Highway 49 attempt to correlate the geologic, mining, historic, 

 scenic, and cultural features encountered as one travels north along the 

 route from Mariposa to Yuba Pass and Sierra Valley. 



The geologic maps, which these notes accompany, form a continuous 

 strip through the Sierran Gold Belt, and cover an area a few miles wide 

 on either side of Highway 49. In the preparation of the maps and the 

 descriptions, material was assembled from various sources of information, 

 published and unpublished, supplemented by field notes. To facilitate the 

 reading of these notes while traveling, footnote references have been 

 omitted, but sources of information are acknowledged in the preface ta 

 this volume. 



MARIPOSA TO COULTERVILLE MAP 1 



The junction of Highways 140 and 49, one-half mile north of the 

 town of Mariposa, marks the southern terminus of Highway 49. Mariposa,- 

 the county seat of Mariposa County, is on the tourist route to Yosemite 

 Valley, and its fine old County Courthouse, a white frame structure 

 erected in 1854, has been in use continuously since that date. The town 

 lies at an elevation slightly above 2000 feet in a northwesterly trending 

 valley bordered to east and west by ridges of moderate height. Vegetation 

 in this region is sparce and is composed largely of digger pines, small 

 oak trees, and patches of chaparral. There are a few small stands of 

 yellow pine on protected north slopes southwest of Mariposa. Early day 

 logging operations removed much of the timber in this region. 



A mile south of Mariposa, in the vicinity of the County Fair Grounds, 

 are the dumps and partly caved workings of the Mariposa mine, which 

 was discovered in 1849 by Kit Carson and two associates. As early as 

 July 1849, Palmer, Cook, and Company were running a stamp mill on 

 ere from the Mariposa mine. In 1859 John C. Fremont wrested the title 

 to the mine from its original owners when accorded title to the Las Mari- 

 posas grant of 44,000 acres. Mines of the Las Mariposas grant also included 

 the Pine Tree, Josephine, Princeton, and many minor workings such as 

 the Penon Blanco claim. The latter is one of the longest claims on record, 

 title having been recorded before length limitations on mining claims 

 became law. The Mariposa mine had its heyday between 1900 and 1915, 

 1901 being the peak year. Estimated total production for the mine is 

 $2,193,205. Workings reached a depth of about 1550 feet along a 60 to 

 70 incline or about 1350 feet vertically. The veins lie in meta-augite 

 andesite of the Penon Blanco formation, locally called greenstone. 



(35) 



