NO. 24 PTARMIGANIA STRATA RESSER 3 



LOCATION AND TOPOGRAPHY 



The location and general topographic expression of the Wasatch 

 Mountains are well known. The conspicuous rampart of these 

 mountains east of Great Salt Lake and the ranges in northeastern 

 Utah and southeastern Idaho are familiar. In this paper we are 

 concerned only with the northern portion of these mountains from 

 the vicinity of Brigham to their termini in Idaho. 



The high, abrupt slope of the Wasatch Mountains facing Great 

 Salt Lake Valley continues from Salt Lake City northward to Malad, 

 which is about 15 miles north of the Idaho State line. Several gaps 

 interrupt the range, the most conspicuous being formed by the Bear 

 River as it breaks through from Cache Valley. North of Malad the 

 less elevated Bannock Range continues the trend of the Wasatch 

 Mountains but is composed of younger strata. 



Between Ogden and Brigham many ridges occupy an area more 

 than 25 miles wide. In the eastern portion of this area the ridges 

 are grouped together as the Bear River Range, which extends thence 

 north through Utah and into Idaho as far as Soda Springs, some 

 40 miles north of the Idaho boundary. 



Cache Valley lies between the two prongs, the Wasatch proper 

 on the west and the Bear River Range on the east. Cache Valley has 

 a nearly level floor about 4,500 feet above sea level. East of it the 

 Bear River Range rises abruptly to altitudes of about 9,000 feet, 

 and on the west the Wasatch also rises steeply to about the same 

 height. Thus there is a V-shaped mountain mass that surrounds 

 Cache Valley, and is in turn bounded on the west by Salt Lake 

 Valley and on the east by Bear Lake and Valley. 



GENERAL GEOLOGY 



As shown by the geological map of Utah, crystalline pre-Cambrian 

 rocks occupy the front of the Wasatch Mountains between Salt Lake 

 City and Ogden. Eastward these rocks are succeeded immediately by 

 Tertiary beds. From Ogden to Brigham the Willard overthrust 

 puts Cambrian rocks on the face of the range in contact with a belt 

 of pre-Cambrian rocks. This belt of crystalline rocks is overlain on 

 the east by Cambrian and younger Paleozoic strata in normal sequence. 

 Since the strike here is northwesterly at an angle to the mountain 

 front the Cambrian rocks again come to the front of the range north 

 of Brigham for a distance of several miles, their place then being 

 taken by younger Paleozoic beds. North of the Bear River Gap 



