Structural data and field relationships in the southern part of the Mogollon Plateau volcanic province of southwestern New Mexico show that significant shallow intrusive activity occurred during early Tertiary time along a north-northeast–trending belt 1.5 to 3.0 km wide and 35 to 45 km long. Magmas were injected into Paleozoic-Mesozoic sedimentary strata, causing arching and other deformation of the country rocks. The resulting structure, called the Santa Rita-Hanover axis, initially had considerable topographic relief. It acted as a barrier to mid-Tertiary volcanic flows, causing the development of two volcanic subprovinces.

The Santa Rita and Hanover-Fierro intrusions define the southern part of the axis and are associated with large deposits of copper, zinc, and iron, which give the structure major economic importance. Other ore deposits may also be associated with the axis.

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