334 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



The office-work thus acquired an exceptional importance 

 as compared with the field-work, which, for the season of 

 1878, was placed in charge of Mr. C. K. Gilbert, his principal 

 assistants being Messrs. J. H. Renshaw, O. D. Wheeler, and 

 S. H. Bodfish. 



Taking the field at Gunnison, Utah, in the early part of 

 August, the work was carried on by four independent par- 

 ties till the middle of December, when the advance of winter 

 made it necessary to disband them. 



The Kanab base-line, four and one-third miles long, has 

 been carefully remeasured, with a probable error of 1.5 inch- 

 es, as well as the southern portion of the chain of triangles 

 connecting it with the Gunnison base-line. The main chain of 

 triangulation, consisting of eight quadrilaterals, one triangle, 

 and one pentagon, is now ready for discussion. At each end 

 of the chain a base-line has been measured, and an astronom- 

 ical determination has been made of latitude, longitude, and 

 azimuth. The most southerly points visited were Mount San 

 Francisco and Mount Floyd, volcanic peaks on the Colorado 

 plateau south of the Grand Canon. Southern Utah is not 

 well adapted for triangulation. Its principal eminences are 

 table-lands or plateaus covered with timber, there being very 

 few sharp peaks readily distinguishable from all directions. 



The work of Mr. Renshaw's party witli plane-table and 

 orograph embraces all of the region lying south of the Grand 

 Cailon in Sections 105 and 106, covering about 7500 square 

 miles. This field comprised a portion of what is known as 

 the Colorado Plateau, a high table-land lying immediately 

 south of the Colorado River, which there runs westwardly 

 at the bottom of a deep chasm. On the southern edge of 

 the plateau there are innumerable extinct volcanoes, the 

 ground being covered by a forest of pine, the most valuable 

 tract of timber in Arizona. The northern edo-e is lower, and 

 is bare of timber. Near the Colorado Cailon it is broken by 

 gorges, and is difficult of access, but in other directions there 

 is little impediment to travel. Water is scarce, and is found 

 only in pockets and small springs, there being none available 

 for irrigation. The only wealth of the country lies in timber 

 and grass. West of the plateau, Mr. Kenshaw's map includes 

 a portion of Ilualapai valley and the adjacent mountains. 

 This region is almost an absolute desert, water being so 



