After completing his doctorate studies, Lothrop worked field excavations in the
Yucatan and
Guatemala under the employment of the Carnegie Institution's Historical Division. His research resulted in the 1924 publishing of the monograph of his mapping of the Mayan Ruin of
Tulum. From 1924 until the end of the
stock market crash in 1929, Lothrop was employed by the Museum of the American Indian, Heye Foundation. It was during 1929 also that he married his second wife, Eleanor Bachman of
Philadelphia. His work while he was on staff at the museum was also focused on
Latin America and it was during this time that he established a relationship with Fernando Marquez Miranda. It was through this relationship that Lothrop was one of the few foreigners allowed to conduct excavations in Argentine Territory.
Notable excavations Sitio Conte In the 1930s, after the closing of the museum, Lothrop returned to the Peabody Museum staff as field director of the
Sitio Conte in Central Panama.
Stone spheres of Costa Rica In 1943, through a publication of
American Antiquity by
Doris Stone, Lothrop first encountered the mysterious stone spheres. In 1948, he and his wife met up with Doris Stone and she collaborated with them, setting them up with a place to excavate. The stone spheres are a topic of discussion, concerning how these objects were formed and by whom. Lothrop's research resulted in the theory that the balls were placed in alignments significant astronomically. During his research Lothrop recorded 186 balls as reported in his 1963 publication,
Archaeology of the Diquís Delta. Lothrop determined that the spheres were formed over many centuries, suggesting a cultural practice and continuity over an extended period of time. His conclusions were based on analyzing the pottery types. ==Notable accomplishments==