104 METHOD OF COMPILING THE MAP. 
points, which it is proposed to correct, in longitude, by lunar culminations, and such absolute 
observations as may be conveniently obtained. Such a position at the mouth of Fontaine qui 
Bouit, on the Arkarsas river, will be a good point of reference for the longitudes along the 
foot of the mountains. In passing by the Utah to the southern portion of the Great Salt lake, 
we shall have an opportunity to verify our longitudes in that quarter; and as, in the course of 
our exploration, we shall touch upon several points previously determined along the western 
limit of our recent journey, we shall probably be able to form a reasonably correct frame on 
which to base the construction of a general map of the country.’’ 
In Captain Frémont’s memoir and map on Oregon and Lower California will be found the 
astronomical results of this expedition from the mouth of Fontaine qui Bouit creek westward. 
No topographical explorer has since visited points along his routes with means capable of 
detecting any errors in his determinations, and they have been generally adopted. The mouth 
of Fontaine qui Bouit creek was placed on the first map in longitude 105°; on the second, 
according to moon culminations, in 104° 42’ 41". The longitude determined at Great Salt 
lake, and at Lassen’s farm on Deer creek, California, by moon culminations, confirmed his first 
determinations of positions in these regions as given on his previous map. The position for 
Lassen’s is only about 5’ too far east, as since determined. The correction which Captain 
Frémont found at Fontaine qui Bouit, viz: 17’ east, if used to correct the ‘‘longitudes along 
the foot of the mountains, as given on the map of explorations in 1842-43-44, would place 
St. Vrain’s Fort in longitude 104° 55’, and Fort Laramie in longitude 104° 30’, and this last 
agrees nearly with that adopted on Stansbury’s map.’’ (See note of Lieutenant Gunnison, 
page 302, Stansbury’s Report.) But Mr. Preuss, in constructing the map of 1848, puts Fort 
Laramie still further east, viz: in longitude 104° 25’, and St. Vrain’s Fort in longitude 104° 47’, 
moving these points further east, it seems to me, than the correction obtained at the mouth of 
Fontaine qui Bouit creek demanded. I have taken Fort Laramie in longitude 104° 30’,* and 
St. Vrain’s Fort in longitude 104° 55’. Captain Frémont’s route, in 1843, from St. Vrain’s 
Fort west to his station of September 13, on Bear river, had to be elongated from what it is 
represented on the map of 1844, and shortened from what it is on the one of 1848. I retained 
the position of the crossing of the north of the Platte (longitude 107° 10’) as given on the map 
of 1848, Lieutenant Gunnison having adopted it in constructing Stansbury’s map. This is 
nearly the position it would have by distributing the correction which I have applied to St. 
Vrain’s Fort between that point and Frémont’s station of September 13, 1843. This station of 
September 13, depends for its longitude on an occultation of t Arietes, and to it all the points 
of the route along Snake river, and the Columbia as far as the Dalles, are referred by chrono- 
metric differences. Captain Frémont’s routes south of Lieutenant Beckwith’s trail, in Utah, 
have all been reduced to our map as given on his map of 1848, his position for the point where 
the Santa Fé trail leaves the Mojave agreeing with the best recent determinations. In putting 
down Captain Frémont’s route from Bent’s Old Fort east along the Smoky Hill Fork of the 
Kansas, as given on his map of routes in 1842, 1843, and 1844, I have moved his position of 
Bent’s Old Fort from 103° 45’ to 103° 24’ 30”, and of the point where he struck the Santa Fé 
road from 96° 58’ to 97° 12’, thus shortening this portion of his route by 34 in longitude. St. 
Vrain’s Fort having been moved 17’ east, and the mouth of the Republican Fork 14’ west, 
(Fort Riley from 96° 30 to 96° 44’,) the intervening portion of his route, via the Republican 
Fork, was 31’ shorter in longitude than represented on his map of routes 1843~ 44. 
* Bight nights’ observations made by me in 1857 with a 26-inch transit, on moon culminations, gave for the result 
104° 30’ 36”, 
