The Maya Area is of outstanding archaeological importance because its early inhabitants achieved the highest civilization in pre-Columbian America. The early Maya and Mexicans surpassed other highly developed pre-Columbian American cultures because they possessed a form of writing and an intricate calendrical system. While the question of priority and derivation of culture in the Mexican-Maya area is still a moot one, there is no doubt that the Maya developed writing, representational art, and the sciences of mathematics and astronomy to a degree of excellence far beyond that attained by the Mexicans.

The Maya lived, before the Conquest as today, in Yucatan and the country south of it. We have little evidence concerning the archaic or earliest peoples of this region. We know that in the southern part there was such a cultural substratum, identified by modelled figurines and distinctive pottery.

Aerial photographs were employed in archaeological work as early as 1880. The results proved the value of aerial photographs, but the methods of raising a camera aloft were unsatisfactory until the invention of the airplane. Also the quality of cameras and sensitive plates was not very good in the early days. For these reasons, aerial photography was applied to archaeology infrequently until after the World War.

Military operations accelerated the development of airplanes. Cameras were designed especially for air use and the quality of lenses and plates was improved greatly. This resulted in a rapid growth of aerial photography. The applications of aerial photographs were limited almost entirely to military uses, including mapping. The post-war development followed similar lines. Aerial photography was found to be indispensable to military operations and all air forces devoted considerable attention to this specialty.

Archaeology in the California area has been notoriously slow to recover cultural sequences. In part this is due to most of the earlier explorations having been conducted without sense of genuine scientific problem, as in the first stages of work in so many other regions. But in even larger measure the delay in discovering positive time changes is the result of difficulties inherent in the archaeological data of the area. Mostly there is no pottery at all. The historic cultures being simple, their artifact inventory is fairly limited and lacking in specialized types. Except in the Santa Barbara region, the numerical yield of specimen data is low for volume of soil moved. The San Francisco Bay mounds, for instance, tend to furnish only about one artifact, whole or broken, per cubic yard dug. This is probably not far from the average productivity the state over, the Santa Barbara coast and islands alone omitted.

Some of the most common artifacts found on all of the ancient Hohokam sites in southern Arizona, and upon many of the Pueblo sites further to the north in both Arizona and New Mexico, are the thin, well-made bracelets, earrings and finger rings, fashioned from the Glycimeris shell. The broken fragments of these specimens are particularly noticeable in the great trash heaps marking the Hohokam villages. The normal type is a plain, smoothly-cut, well-polished circlet of shell, usually perforated with a small hole at the apex of the hinge.

Although archaeologists have long been familiar with these, and know that the shells from which they were made are found in the Gulf of California, the origin of the artifacts themselves has not been established. It has been inferred that the Indians of the interior obtained the complete shells in trade, or that in ancient times the inhabitants of the Gila and Salt valleys traveled to the Gulf, a nine days' journey on foot, even as the Pima and Papago have resorted thither for salt in more recent historic times.

The origin and culture of the older archaeological material taken from Ludlow Cave, Cave Hills, Harding County, South Dakota, in July, 1920, has been subjected to some discussion and speculation. The cave was named after William Ludlow, Chief Army Engineer of the Department of Dakota, who visited it in 1874 while accompanying the Custer Expedition from Fort Abraham Lincoln to the Black Hills.

The cave is located in the northeast quarter of section 12, township 21, range 5 W, in the extreme northwest corner of the state in the Sioux Forest Reserve. Geologically, it is in the Ludlow Division of the Laramie formation, Upper Cretaceous Period. It is irregular in shape, extends back thirty-nine feet, and is sixteen feet wide and ten feet high. The entrance was partially blocked by rocks, each weighing several tons, which had fallen from above.