The fi rst geologic map of Sonora

Resumen

The 1888 publication by
José Guadalupe Aguilera Serrano about the 3 May 1887 Sonora, Mexico
earthquake contains the earliest geologic map of Sonora, a
1:1,000,000 scale color map with six cartographic units, reproduced
in this paper. On the map, which covers ~20,000 km2 of northeastern
Sonora, and in the accompanying article, Aguilera delimited and
described parts of what is now known as the Jaralito and Oposura
batholiths and assigned them, remarkably, an Eocene age. The map
unit of volcanic rocks belongs mostly to the vast cover of the
middle Tertiary Sierra Madre Occidental volcanic province and the
units of Pliocene and Quaternary rocks to the fi ll of extensional
basins. Aguilera assigned a Quaternary age to the basalt fl ows in
the Moctezuma and San Bernardino valleys, which he described as
covering the alluvium of these valleys. The rocks of the Pliocene
map unit were described by Aguilera as an indurated conglomerate
dipping 20° S, overlain with angular unconformity by alluvium, and
most of its clasts being of volcanic origin; this unit is now known
as the Báucarit Formation of Miocene age. The Cretaceous map unit,
described by Aguilera as ash grey, compact, and fossiliferous
limestone beds belonging very probably to the Comanche series, is
now known as the Lower Cretaceous Mural Limestone. Aguilera’s map
covers a series of north-south trending mountain ranges separated by
the Moctezuma, Bavispe, San Bernardino, Fronteras, and Agua Prieta
River valleys, a landscape pattern typical of the Basin and Range
physiographic province. Aguilera described this transition zone
between the plateau of the Sierra Madre Occidental in the east and
the lowlands in the west as a large-scale staircase pattern, with
the steep, fault-bounded side of the mountain ranges always facing
west. A rare photograph by Camillus S. Fly possibly shows Aguilera
and his fi eld party near Bavispe, Sonora in August 1887.