From the Plains. On Sunday, the 24th ult., two men and a boy, arrived in this town from Oregon. These gentlemen represent the emigration to Oregon, California, and Salt Lake, getting along very well. They met Elder Hyde, Judge Brocchus, and company on the 7th, three hundred miles this side of the Valley, enjoying good health and spirits. The other companies of Saints, who left here this season, were in succession behind, prosecuting their journey with reasonable speed. The grass on the plains is represented to be good, except in some place where camps had previously been; in those places it was rather scarce.