When first mapped in 1926, Hollywood Mounds consisted of a large pyramidal platform mound enclosed on three sides by a series of smaller mounds forming an earthen embankment. Three additional mounds were located toward the eastern boundary of the site, along the edge of Mound Bayou. Together, the boundary mounds and the bayou define a rectangular area of approximately 1.5 hectares. Today, Mound A and three small boundary mounds toward the north are visible, but most of the boundary mounds and three mounds to the east have been plowed down since the mid-twentieth century.
Recently, professional archaeologists have used non-destructive geophysical survey techniques and targeted excavations to determine the history of mound building at the site. One of these techniques, magnetic gradiometry, has successfully located buried features at the site, including several boundary mounds no longer visible from the surface. The mounds exhibit a distinct magnetic signature due to the fact that the buildings on their summits were burned, and the remains were then pushed over the edge of the mounds, creating a halo around each mound with enhanced magnetic properties. As many as 27 former mounds have been identified in this way, many of which correspond to the locations of mounds mapped in the early twentieth century.
Excavations at the site have determined that the small boundary mounds were the first earthworks built at the location by Native American people. The mounds were built during the Mississippian period, sometime after about AD 1300. Afterwards, the plaza area defined by the boundary mounds was artificially raised and flattened, a process that involved moving more dirt than all the mounds at the site combined. Sometime after the completion of the plaza, or perhaps in conjunction with its construction, Mississippian people built Mound A, the site's central feature. This sequence of building happened quickly at Hollywood, perhaps over the course of about 200 years.
