“The exodus each year from the jumping-off places on the Missouri River began on the approximate date when it was agreed that grass would be sufficiently green on the plains to support the animals. . . .
A drouth could delay departures alarmingly, increasing prospects of getting snowbound in California’s mountains in the autumn; but a rainy season could slow things down, too, as wagons mired in the mud before they were well started . . . But give or take a week or two, a good starting target date for departure from any of the jump-offs was April 15, for arrival at (or opposite) Fort Kearny, May 15, at Fort Laramie, June 15, and at South Pass, July 4.
Arrival at a destination in Oregon or California by September 1 was hoped for, but October 1, well ahead of snow in the Sierra Nevadas, was considered satisfactory. An ideal passage would be four months, or 120 days, April 15 to August 15. . . . [F]our and a half months, from April 15 to September 1, was more nearly par for the course, while painful trips of up to six months’ duration have been noted. . . .Most of the really late comers spent a miserable time wintering at Fort Laramie or Salt Lake City.”