Assessing Early Spanish Explorer Routes Through Authentication of Rock Inscriptions

Rock inscriptions containing both names and calendar dates provide place-specific data on travels of explorers, if those inscriptions are truly authentic. We exemplify here a new strategy for determining the authenticity of inscriptions in arid environments in two case studies. One is an inscription purportedly created during the Marcos de Niza expedition of 1539 through Arizona. The other might have been made by the Dominguez-Escalante expedition of 1776 through the Colorado Plateau and Great Basin. The rock inscription in Phoenix, Arizona, "Fr Marcos de Niza corona todo el nuebo Mexico a su costa ano de 1539," is likely not authentic. Although the Marcos de Niza petroglyph was manufactured before the use of leaded gasoline about 1922, it was made after the Little Ice Age ended in the mid-nineteenth century. In contrast, the engraving "Paso Por Aqui-Año 1776" near Lake Powell's Padre Bay in Glen Canyon National Recreation Area has a lead profile indicating that the engraving predates twentieth-century pollution and also contains a Little Ice Age signal, evidence that the engraving is likely authentic. Nearby graffiti and natural weathering often endangers rock inscriptions, necessitating conservation efforts of authentic engravings. Conservation efforts to protect the delicate condition of the Lake Powell engraving are justified by these findings. In contrast, unnecessary expenditures and effort can result from work on engravings that are not authentic.