Establishing the exact date of the beginning of geological studies is difficult. The discovery of “sepulchers of giants” has been taken as such, as the large vertebrate fossils found in the Cenozoic deposits of the Pampas were called in the American colonies in the 16th century. This led to great discussions about their meaning and allowed progress in the knowledge of these remains. It was not until 1751 that the first precise description of these findings was made, preserved under thick layers of ash. Numerous other discoveries followed until an almost complete specimen of Megatherium was found in Lujan, studied in 1793 in Spain, and classified as such by Cuvier in 1804. It was one of the first large fossil mammals found in the world. The first precise geological descriptions of the lithology and structure of the outcropping rocks from the Sierras Pampeanas to Bolivia were made by the German geologist Anton Zacharias Helms, published in 1798 and later translated into English and French. These observations were followed by those of Tadeo Haenke, a naturalist born in Bohemia who, after participating in the Malaspina Expedition, settled in Cochabamba, part of the Viceroyalty of the Río de la Plata at that time. He published numerous contributions at the beginning of the nineteenth century, although many of his descriptions remained unpublished. The first specific geological study of the United Provinces of the Río de la Plata was carried out in 1819 by Dámaso Antonio Larrañaga, a self-taught Río de la Plata native. His Escritos were published a century later.