MAPS ACCOMPANYING THE REPORT. 
13 
that this is about 121° 22' 19", which differs more than twenty miles from that deduced from 
the first observation. I have, therefore, adhered to the longitude given by my field work, 
which-is intermediate between the two, hut much nearer that to which Col. Fremont has given 
the preference. 
The longitude of Fort Vancouver has been laid down as given on the latest Land Office map of 
Oregon Territory, because detailed surveys have been made between the fort and Salem, the 
position of which, as already explained, has been determined with approximate accuracy. This 
location of Fort Vancouver is about seven miles east of that of Capt. Wilkes, whose longitude 
has been adopted by Col. Fremont on his map of Oregon and California, and by Captain 
McClellan. 
Considerable difficulty has been found in locating the Cascades of the Columbia with respect 
to longitude. Gov. Stevens adopted the position given by Capt. Wilkes, which is 21 miles 
further towards the west than that of Col. Fremont, who observed an occultation of Jupiter’s 
first satellite, on November 11, 1843, at a point estimated at 15 miles below the Cascades. 
There is now a line of steamboats plying from Vancouver to the Cascades, and thence to Fort 
Dalles. Capt. W. B. Wells, the chief proprietor of the line, and all other persons whom I 
questioned about the matter, declared that the Cascades were about equally distant from Van¬ 
couver and the Dalles, by the course of the river. Col. Fremont has so indicated it upon his 
map ; hut Capt. Wilkes makes the distance from the Cascades to the Dalles nearly double that 
from the Cascades to Vancouver. Considering the great discrepancies between these two 
authorities, and believing that the many hundred trips of the steamboats must have enabled 
the owner to estimate the comparative distances with tolerable accuracy, I have placed, on the 
accompanying map, the Cascades midway between Vancouver and Fort Dalles by the course of 
the river. This location is 10 miles west of that of Col. Fremont and 11 miles east of that 
of Capt. Wilkes. 
I have indicated on the map, positions for Mount Adams and Mount St. Helen’s—the former 
given by eight and the latter by six good hearings from well determined points in the Des 
Chutes and Willamette valleys, and among the Cascade mountains. Each of these positions 
differs about 12 miles from that given by Gov. Stevens. 
It has been considered desirable to make the maps as complete as possible, by indicating the 
topography of the country remote from our trail, whenever reliable information as to its char¬ 
acter could be obtained. The Pacific coast has, therefore, been laid down as given on the latest 
United States Coast Survey maps. The most recent Land Office maps of Oregon and California 
have been adopted as authority for the settled portion of the country, except in the vicinity of 
our trails, where the topography is, of course, given from our own field notes, checked by 
astronomical observations. 
The map of Lieut. E. G. Beckwith, 3d artillery, illustrating his explorations for a railroad 
route near the 41st parallel of north latitude, has been followed for the region bordering Pit 
river, below the mouth of Canoe creek. 
The topography south of Suisun Bay has been taken from the map of a survey in California, 
made, in connection with examinations for railroad routes to the Pacific ocean, by Lieut. K. S. 
Williamson, Topographical Engineers, in 1853. 
Summer lake, the northern and western shores of Upper Klamath lake, the chief tributary 
of Klamath marsh, and the Columbia river, east of the Dalles, have been laid down as given 
by Colonel J. C. Frdmont on his map of Oregon and Upper California. 
