The Mammoth Hot Springs Post Office in Yellowstone National Park was constructed between 1935 and 1938 and exemplifies French Renaissance Moderne architecture. Its travertine-adorned lobby features stone sourced from a quarry near the park's north entrance. Flanking the entrance are two limestone bear sculptures, added in 1941, crafted by artist Gladys Caldwell Fisher. In 1987, the Mammoth Hot Springs Post Office was listed on the National Register of Historic Places, recognized alongside 11 other Wyoming post offices built between 1908 and 1939. This designation highlights the building's architectural significance and its role in reflecting the federal government's presence during that era. The post office is still in operation and is open year-round, Monday through Friday from 8:30 am to 5 pm (excluding federal holidays). Its lobby remains accessible 24/7. It is right by the Albright Visitor Center in the Mammoth Hot Springs area.