The hot spring north of Delta, Utah, is of particular interest because it has yielded commercial manganese ore; 715 tons of manganese oxide ore that averaged 20% manganese and 0.26% sulphur is recorded. The deposits occur as a thin bed and as lenses and nodules in a dome about 1,600 feet across and 15 feet high that has been formed subsequent to the dessication of Pleistocene Lake Bonneville. The alkaline hot waters, which reach temperatures of 182 degrees F. and have a total discharge of over 1,200 gallons a minute, average 3,900 parts per million in dissolved solids, with NaCl, CaSO 4 , MgCl 2 , and CaCO 3 . Five complete analyses show a manganese content of from 0 to 1.2 parts per million. Nevertheless, no appreciable manganese seems to be precipitating at present. The bed of manganese and iron oxides is scarcely more than a foot thick and is mostly covered by porous calcite. The ore is a porous aggregate of psilomelane and pyrolusite in which the vugs are lined with limonite. These minerals have been formed through the action of hot alkaline solutions over a long period; the original mineral was probably wad. The barium oxide is believed to be chemically combined with the manganese oxides. Probably all these materials have been leached from underlying rocks or deposits by hot circulating groundwaters and may not have a magmatic source.