136 



METEOROLOGY OF THE FIELD EXPLORED. 



during the same period, February 7 to 15, and February 19 to 24, the average temperature of 

 Puget sound was about 42 ; yet the snow in Clark s fork increased nowhere more than one 

 foot, and that uniformly in the wooded portion of the route. While these are the probable 

 conclusions from what is known, the question ought not to be considered settled till further exami 

 nations are made. 



But I have no question that much of the moisture in all the winter months is deposited in rain 

 in the mountain passes; and this conclusion must be reached by every observer of the effect of the 

 warm rains of the winter on the surrounding mountains, causing in November, in December, and 

 in February (I speak of what was observed last winter) large masses of snow entirely to dis 

 appear. The mountains change from day to day. The whole surface of the mountain slopes 

 will be covered one day with snow, and the next large portions will disappear, in consequence 

 of the genial rains. 



I much regret that Lieutenant Grover did not receive my orders in time to go through the 

 pass in March. 



I have thus fully gone into the reasons which have convinced me that there will not be suffi 

 cient snow in this pass to obstruct the passage of cars, and that frequently the pass is practicable 

 for horses all through the winter. I believe a wagon-road can be used through that pass with but 

 little labor all winter. It seems to me that the conclusions to which I have come, from actual 

 observations, are to be drawn ; from the extreme narrowness of the mountain range at the pass, 

 only about seven and a half miles ; from its absolute altitude, only 3,500 feet, being more than 

 2,3SS feet above Vancouver ; from the open character of the valleys on both sides ; and from the 

 mild character of the climate of Puget sound, in close proximity, causing much of the moisture 

 to be deposited in rain. Should the grades be found good on the western slope, of which I am 

 confident, the Snoqualme Pass must furnish the entrance to the sound of the trunk line of the 

 northern route ; and it becomes important, to satisfy the skeptical, to test thoroughly the ques 

 tions of snow as well as of grades. In the event of the continuation of the survey, I would recom 

 mend establishing a winter post near that pass. At all events, it is unquestionable that no obstruc 

 tions from snow exist in the passes of the Rocky mountains, and of the route of Clark s fork, 

 the Spokane plain, the Columbia and Cowlitz valleys, to Puget sound. 



For more information in reference to this subject I will refer you to Lieutenant Grover s report 

 of his winter trip from Fort Benton to Wallah- Wall ah, marked I 36 ; to Mr. Tinkham s report, 

 marked I 37 ; and to Mr. Mullari s report of his reconnaissance to Fort Hall, marked G 25 ; as 

 also to the letters of Mr. Rice, Mr. Sibley, and Mr. Culbertson, marked I 38, in the appendix. 



No. 1. MEAN TEMPERATURE FOR EACH OF THE LAST FIVE YEARS. 

 Fort Sndliny latitude 45. 



