Work was continued by Joaquín Matilló, Allan L. Bryan and Jorge Espinosa in the 1960s and 1970s. Allan L. Bryan, from the University of Alberta, used radiocarbon dating to determine the age of soil humates, from a buried soil directly underlying the footprints, to 5,945±145 radiocarbon years Before Present. Based upon this date, he estimated that the footprints dated to about 5,000 Before Present. But, later dating of the volcanic deposits in which they occur, known as the Masaya Triple Layer, demonstrated that the fossil tracks are only about 2,120 ± 120 years old. In 1978, the Nicaraguan researcher Jorge Espinosa continued the excavation near the termination of the original excavation. He uncovered more footprints at a depth of 4 meters. The track is believed to continue further.