Significance of an aeromagnetic anomaly in the southwestern part of the Blue Range primitive area, Arizona-New Mexico

In the Autumn of 1968 the U.S. Geological Survey flew a detailed aerial magnetic survey of the southwesternmost part of the Blue Range primitive area between Lat 33°21'00" and 33°29'00" N. and Long 109°15'00" and 109°22'30" W. The survey was intended to define more precisely a positive magnetic anomaly that had been found from an earlier survey (Ratte and others, 1969, Pl. 1 and p. E30-31) by reducing the original flight elevation from 10,500 feet to 8,000 feet and the flight line spacing from 1 mile to 1/2 mile. The results of the more detailed survey are shown in the accompanying figure (fig. 1). The anomaly in question lies in the center of the map and has a peak value of 915 gammas and a closure of approximately 460 gammas. On the earlier map (Ratte and others, op. cit.) the closure is approximately 80 gammas.