Where did the gold come from? Ancient vents and fractures and vestiges of the old Ortiz volcano are the ultimate sources of the gold. The old Dolores town site is near the middle of the Dolores vent breccia - a geologic pipe of broken and naturally re-cemented rock. South of Dolores and east of the Preserve, a large, now-abandoned open pit gold mine marks the source of the Cunningham Gulch gold - found in the brecciated margins of a rock (trachyte-latite) vent.
If the breccia of a geological vent is auriferous (contains gold) then the gravel down slope from that breccia vent should be excellent placer* ground. Correspondingly, if you find good placer ground, then look up slope for the source of the gold, i.e. the mother lode. If that gold is angular and wiry, an indication it has not been banged around by traveling far, the mother lode should be near by. When you find a mother lode, as in the Ortiz Mountains sometime around 1830 a local resident named Luís Lovato probably did, it will often appear as twisting slices of rust-colored iron-rich porous quartz within a geological vent or along a fault line. What would eventually become known as the “Old Ortiz Lode” was described as “distinct quartz fissure veins and stringers.” In Lovato’s case the intertwined rusty dark brown-black and milky white quartz rock contained tiny (and occasionally not so tiny) flakes, scales, and threads of free milling metallic gold. A visit to the Ortiz Mountains Educational Preserve will usually include a stop at the original Old Ortiz Lode.
Much later, in 1896, J.T. McLaughlin, talking about the geology of the placer land immediately to the east of Dolores, said, “On the east side of the range are large fields of rich placers – decomposed quartz in the form of sand and gravel, which have inundated most of the entire eastern slope. Here are thousands of millions of cubic yards of gold bearing material that rests on soft sandstone. These deposits were largely made in a past age, but after the mountains had uplifted and had afforded great quantities of gold bearing material which was freed by the rapid erosion of the country rock.... Just above the main eastern dyke and paralleling it for several miles, will probably be found the richest ‘dry placer’ deposit in the entire field.”
“Most placer gold deposits in New Mexico,” says Maureen Johnson, “are derived from gold-bearing mineralized areas in Tertiary intrusive rocks, and occur in gravels of alluvial fans, gulches, and rivers adjacent to the source.” ... “The most productive lode deposits throughout the State are the fissure veins in Tertiary intrusive rocks...” Ms. Johnson continues with specific reference to the Ortiz: “Placers are found on the eastern and southern slopes of the Ortiz Mountains; the gold occurs in both creek and mesa gravels. The richest gravels are found on the eastern slope of the mountains in the vicinity of Dolores and Cunningham Gulch; here, the gold is in mesa gravels that are the upper part of an old debris fan formed at the mouth of Cunningham Gulch. Substantial amounts of gold were also recovered from creek gravels in Dolores Gulch and Arroyo Viejo.”
The story of people in the Ortiz Mountains is overwhelmingly a story of gold. These mountains were the location of the first major gold rush in what is now the United States. To discover the full history see “The Gold of the Ortiz Mountains”, 160 pages, 35 maps and illustrations, available from the Santa Fe Botanical Garden.
* Placer: concentrating gold by gravity separation by washing sand and gravel, usually in a large pan. Lode: hard rock mining, requiring that the ore be crushed before it can be processed.
More information on the geology of the Ortiz Mountains - "The Volcano"