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The Toadlena anticline is a doubly plunging asymmetric fold in northeast Arizona and northwest New Mexico. The northwest-southeast-trending structure is approximately 35 mi long and ranges in width from 3 to 6 mi. On the east side of the fold the maximum structural relief is about 5,000 ft and at the south end of the fold the structural closure is about 1,250 ft. The sedimentary rocks in the area range in age from Cambrian through Tertiary and several Tertiary volcanic rock bodies are exposed at the surface. The anticline is on the northeast flank of the Defiance uplift and was formed during the Laramide orogeny.
The Dineh-bi-Keyah field is at the northwest end of the Toadlena anticline. Oil production in this field is from a syenite sill which intruded Lower Pennsylvanian rocks. The sill is of Tertiary age and contains both intercrystalline and fracture porosity. The field was discovered in January 1967, and there are 15 completed oil wells on 160-acre spacing. Initial potential for an individual well was as much as 3,300 bbl/day of oil. Cumulative production to July 1, 1968 was 4,164,871 bbl.
Nonflammable helium-bearing gas is trapped structurally in the Devonian McCracken Sandstone on the Toadlena anticline. There are two areas of accumulation with different gas-water contacts. These areas are separated by a saddle near the Arizona-New Mexico line. To September 1, 1968, 11 wells have tested gas from the McCracken Sandstone. One well, on the south end of the anticline, produced about 11,000 bbl of oil before it was shut in due to an excessive gas-oil ratio.
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