The microscopic and sequential analysis of an early 19th-century Native American Indian calendar stick documents the notation of a precise, nonarithmetric, observational lunar year of 12 months, with evidence for added, subsidiary months. This suggests the use of a thirteenth intercalary month every three years to bring the calendar into phase with a solar device known from the Americas outside of the high Mesoamerican and Andean Civilizations, but it is not derived from these late traditions. The analysis suggests the presence of an underlying observational conceptual base that may have come into the Americas from Asia.