The vast wilderness that comprises the mountainous borderland between Arizona and New Mexico is part of the immense Datil-Mogollon volcanic field. It stretches from the Datil Mountains of New Mexico westward to the Arizona border and then southward to the Gila River. The adjoining southeastern quarter of Arizona is also part of an enormous volcanic field which stretches from the White Mountains southward to the Gila. This volcanic field is essentially a western extension of the Datil-Mogollon field of southwestern New Mexico, but the volcanics in Arizona are younger and more mafic.
The Datil-Mogollon volcanic field consists of a huge pile of mid-Tertiary silicic to andesitic volcanics intruded and overlain by younger Tertiary-Quaternary lavas. In general, the Tertiary volcanics in the Datil-Mogollon field are bimodal in composition. In this case, the two modes are andesite and rhyolite. This bimodal flavor is well demonstrated in the Mogollon Mining District where layers of andesite alternate with flows of rhyolite.
The volcanic terrain of southeastern Arizona consists mostly of Tertiary-Quaternary basalt flows and agglomerates. These volcanics are younger and more mafic than the Datil-Mogollon volcanics to the east. Basalts are notoriously barren of mineral deposits, but in the deep canyons along the southern border of the volcanic field, older, more promising rock is sometimes exposed by erosion. This is the case at Clifton-Morenci.
In New Mexico, the Datil-Mogollon volcanics form an immense pile that contains over 12,000 cubic miles of mid-Tertiary extrusive rocks. There were several generations of volcanism in the area, but most of the activity occurred during Oligocene and Miocene times. The Mogollon Mining District contains the most important precious metal deposits in the Datil-Mogollon volcanic field. The Mogollon ore bodies occur within the interconnecting faults and fractures associated with the ring-fracture zone of the famous Bursum caldera. Here, we find a classic bimodal sequence of andesite and rhyolite, each alternating with the other.
The northern edge of the Datil-Mogollon volcanic field presents a similar situation. The Datil Mountains in northeastern Catron County are a case in point. The eastern portion of the range is composed of rhyolitic ash-flow tuff while the central and western portions are made up of andesitic volcaniclastics. The same association is found west of the Continental Divide. From Quemado westward to the Arizona border, the vast Tertiary volcanic terrain persists until younger volcanic rocks of Quaternary age are encountered near Arizona's White Mountains. These younger lavas are darker and more basic in composition.
The immense volcanic field that comprises the southern border of New Mexico and Arizona and which stretches eastward for a hundred miles or more is the home of the Lost Adams Diggings. Certainly the potential exists for an undiscovered or hidden gold deposit somewhere in this vast wilderness. The search for the Lost Adams mine can be narrowed down to two areas of interest, both of which derive from the original accounts of Adams and John Brewer. Those areas are:o the northern edge of the Datil-Mogollon volcanic field, extending from the Gallinas and Datil Mountains westward along the Continental Divide. o the headwaters of the San Francisco and Black Rivers, somewhere near the Blue Mountains of Arizona.
Any search for the Lost Adams Diggings must take into account the following clues and observations:
Prospectors may want to concentrate on the western half of the Datil Mountains, including the rugged country just north of the range. The broken canyons just west of the Datils should also be investigated. Their proximity to the old abandoned wagon road that once led to Fort Wingate makes them interesting to the prospector. In addition, the western Datils lie only 15 miles southeast of Veteado Draw. This low-lying grassland and the adjoining Newton Draw form the southernmost edge of the North Plains, a catchbasin for whatever rain that falls in this area. Both draws may have served as habitation sites for early Indians, thus providing Adams and company with a campsite surrounded by "abandoned irrigation ditches overgrown with pumpkins". Prospectors should probably concentrate on the canyons and ravines in which older, middle to early-Tertiary volcanics are exposed. Avoid rhyolitic ash-flow tuffs as they are notoriously devoid of mineral deposits.
Prospectors may also want to concentrate on the rugged mountains west of the Mogollon mines, near the headwaters of the San Francisco and Black Rivers. Here, exposed in one of the many deep canyons that slice the mountains, may be a wedge of older, mineralized rock, the source of the Lost Adams gold.