The excavations in Mound B revealed clearly its internal structure (Fig. 3). An old soil surface, unmistakably defined by a dark humic zone, underlay the entire mound at an average elevation of 99 feet, or approximately the same elevation as the modern surface of the floodplain. This evidently represents the surface humic zone (Zone IIc) of the floodplain at the time the mound was built. Yellow-brown sand (Zone IIb) extended below the buried humic zone to an undetermined depth. Zones IIb and IIc beneath the mound contained a few scattered stone chips and an occasional artifact, but there were no concentrations of cultural material. [Illustration: Fig. 4 HARROUN SITE 41 UR 10 MOUND B AREA contour interval = 0.5 feet shading indicates excavated area] Resting directly on the old floodplain surface was the basal structural component of the mound, a rather compact, circular lens of dark brown sand up to a foot or more thick and averaging about 17 feet in diameter. This lens, which contained abundant charcoal, burned clay daub, bone, shell, and a few artifacts, represented the floor level of a house, designated House No. 3. In and above the floor level were the remains of several charred poles, presumably derived from the burned framework of the house. A burned area approximately four feet in diameter in the center of the lens proved to be the remains of a central fire hearth. It was filled with complex lenses of various shades and textures. A large post mold was found beneath the hearth in the approximate center of the house. Completely encircling the house outline was a poorly defined zone of yellow-brown sand which lay directly on the buried surface of the floodplain and extended upward a foot or two where it gradually blended into the upper component of the mound fill. This light-colored sand may have been banked against the outside of the house while it was still standing; or it may have resulted from uneven, subsurface staining by charcoal and other organic material of that portion of the mound lying directly above the house. In any event, it was virtually devoid of cultural material, only a very few stone chips, widely scattered, being found in it. A well defined humic zone, resulting from organic staining after the mound was built, appeared at the surface of the mound. It averaged about 0.5 feet in thickness. Except for the clay in the hearth and in the house floor, the entire mound was constructed of sandy soil like that of the surrounding floodplain, whence it undoubtedly was derived. The depressions on the northwest and southeast sides of the mound are probably the borrow sources for the sandy soil. The clay could have easily been obtained from exposures in the cut banks at the edge of the creek channel. OCCUPATIONAL FEATURES Besides the two possible borrow pits mentioned above, the only occupational feature found at Mound B was House No. 3.