Tomorrow is a holiday in Utah, and many Latter-day Saints beyond its boarder commemorate, or at least remember, the entrance of Brigham Young into the valley. Today, 163 years ago on the day before, many of the Vangaurd company had already made camp in the valley and there was no rest from the transcontinental journey.
Providing an archetype for millions of subsequent prayers in the inter-mountain west, the camp gather at a meeting and “at the opening the brethren united in prayer and asked the Lord to send rain on the land.” 
Thomas Bullock wrote of the meeting and subsequent activities:
Abut ½ past 11 Committee reported, they had staked off, a piece of fine ground 40 rods by 20 for Potatoes—also a suitable place for beans, Corn & buckwheat. the soil is fertile, friable loam, with fine gravel—at 12 o’clock the first furrow was turned by Capt. Taft’s Company—there were 3 Plows & 1 Harrow at work most of the afternoon[.] Tafts Plow got broke. at 2 o’clock the brethren commenced building a dam, & cutting trenches to convey the water , to irrigate the Land—at 4 oclock other brethren commenced mowing the grass, to prepare a turnip patch. 
They cultivated two and half acres that day; then the pioneer company received the answer to their prayer. At six o’clock, the rain came.
- William Clayton, Journal, July 23, 1847. All sources in this post are from the LDS Church Mormon Pioneer Overland Travel, 1847–1868 database.
- Thomas Bullock, Diary, July 23.