Complex sentence: One of those sites, south of Molstad Village near the mouth of the Moreau River, was named Calamity Village, and was partially excavated by Smithsonian archaeologist Oscar L. Mallory, who operated from the Molstad Ranch base camp.
Split into simpler sentences: One of those sites, south of Molstad Village and near the mouth of the Moreau River, was named Calamity Village. It was partially excavated by Smithsonian archaeologist Oscar L. Mallory, who operated from the Molstad Ranch base camp.