This is the largest tributary emptying into the main drainage channel from the west. It rises in the Uinta Mountains, and has a southerly course for 65 miles. The Duchesne River, its western branch, rises in the same mountains, and the two streams unite only a few miles before the Uinta joins the Green. The drainage basin of the Uinta has an area of 1,300 square miles, lying between the altitudes of 4,500 and 7,000 feet above the sea. It has, generally speaking, a regular slope from the foot of the Uinta Mountains to the mouth of the streams, or in a direction toward the southeast. The surface of the basin is greatly diversified, consisting of broad reaches of bottom lands along the rivers; elevated, level, or gently sloping benches, sometimes partially arable, but oftener gravelly barrens; broken, rock-faced terraces; and low cliffs and ridges. It is difficult to estimate the amount of arable land. All the bottom lands are such, and can be easily irrigated. The streams have a rapid fall, but flow near the surface, and no deep cañons are found anywhere in the basin. This renders it possible to conduct the water over considerable areas of bench land, and wherever the soil of these is sufficiently fertile, selections of good farming land can be made. Above the limit in altitude for successful cultivation, large tracts of meadow lands can be irrigated. Those best acquainted with the extent of these classes of land place the arable, including irrigable natural meadow lands, at 40 per cent. of the whole basin. This would give an area of 520 square miles, and I do not think it is an overestimate. The volume of water flowing in the Duchesne River above its junction with Lake Fork was measured in August, 1877, and found to be 1,011 cubic feet per second. The Uinta was measured above its junction with the Duchesne in October, 1877, and then flowed 214 cubic feet per second. These streams all rise in high mountains, from whose summits the snow is never completely melted. The line of highest water is usually in June, but the flow is well sustained through July. After that the volume rapidly decreases, and lowest water occurs in October. The critical period in the irrigation of this basin would occur in August. I think it may safely be assumed that the measurements of the Duchesne and the Uinta represent the flow at the critical period, but that Lake Fork should be doubled. This would give 1,825 cubic feet per second, or enough to irrigate, at the assumed standard, 285 square miles, or 22 per cent. of the whole area of the basin, and indicates the Uinta drainage as one of the best, if not the best, agricultural valley in Utah. ASHLEY FORK.