FROM BL /ICEFOOT TRAIL TO CLARK S FORK. 273 



camp of November 2 to Wallah-Wallah, are from three hundred and thirty-eight to fifteen hun 

 dred feet above the sea. The dividing ridge of the Rocky mountains was, where we crossed 

 it, six thousand and forty-four feet above the sea; a discussion of the observation on which this 

 depends will, however, probably show that the result is too great. The estimates I have made 

 for gradients depend on the barometrical observations. 



This instrument, from the variations it exhibits when observed at different intervals at the same 

 place, cannot be perfectly reliable when but one is used on an extended line ; so that the estimate 

 may, on a detailed survey of the country, prove to be considerably erroneous. 



I have to transmit herewith a report from Lieutenant Arnold, on the route he followed to Fort 

 Colville, and one from Mr. Tinkham, giving an account of a reconnaissance made by him in con 

 nexion with this portion of the survey. Mr. Lander declines reporting to me on the railroad 

 results obtained by him. As you are conversant with all the circumstances of the case, I have 

 to request, that with reference to any report he may render you touching this portion of the sur 

 vey, you adopt such course as you may think proper. 



I am, sir, very respectfully, your most obedient servant, 



A. J. DONELSON, 

 Second Lieutenant of Engineers. 

 Governor I. I. STEVENS, 



Chief of the Northern Pacific Railroad Survey. 



REPORT OF A. W. TINKHAM, GIVING THE RESULT OP EXAMINATIONS AS TO A CUT-OFF FROM THE 



BLACKFOOT TRAIL TO CLARK S FORK. 



OLYMPIA, WASHINGTON TERRITORY, 



February 18, 1854. 



DEAR SIR : As a precautionary measure to secure the safety of my note-book on leaving 

 Wallah- Wallah for my recent passage of the Cascade range, I committed to the charge of Wilson 

 all notes and papers which I had with me, with instructions to proceed to this place by way of 

 Columbia river, anticipating his arrival here considerably in my advance. As he has not arrived, 

 I am stripped of the means of making a report to you of the several reconnaissances conducted 

 under your direction, other than such general reports as I can make from recollection of the country 

 traversed, and of impressions at the time. 



A previous reconnoitring tour had enabled me to determine a very favorable railway route from 

 the departure from Milk River valley, crossing Marias river, passing north of the &quot;Knees,&quot; and, 

 with admirable facilities, continuing along the high prairie neighboring on the Teton river. This 

 location of the line through this section essentially coincides with the result of Mr. Lander s 

 reconnaissance. 



I parted company with you on Monday, the 19th of September, with instructions to proceed 

 up Sun river to such a point as should connect its valley with the previously determined favorable 

 railway line, and then to join you at Dearborn river, or to overtake you should you first reach that 

 point. 



I continued up Sun River valley to the forks of the river. In this vicinity, and leaving 

 altogether the broken ground which the train passed over after leaving Sun river, I found the 

 desired facilities for connecting the railway line with the line east. Sun river continues to have a 

 broad and open valley, and near the forks, where I propose the crossing of the valley, the country 

 slopes off gradually from either side of the stream, and affords a fine opportunity for an easy 

 passage of the river, and for making ground in the approaches to the mountain pass alreadj near 

 by. The passage of the railway line here brings it into favorable position with reference to the 

 ascent to the pass. The high, smooth plain south of the south fork of Sun river, which the line 

 35 / 



