Giant Drill Core

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From a historical marker:

Shaft Drill Core 1935-36
Experimental vertical shaft 5 ft in diameter to 1125 ft depth through serpentine and gabbro at Idaho-Maryland Gold Mine, Grass Valley. Machinery invented by J.B. newsom. Greatest drilled footage 21 ft in three days. Core weight 11 tones. Donated to Nevada City by Kenneth E Baker.

The Idaho-Maryland Mine Project published a document in 2021 that contained some additional details:

In the 1930s and 1940s, the Idaho-Maryland Mine was the second-largest underground gold mine in California, behind the Empire Mine. Between 1930 and 1940, the Idaho-Maryland and Brunswick Mines yielded 2,186,381 tons of ore, equating to $26.76 million in extracted materials. Additionally, the Idaho-Maryland Mine developed a new method of sinking shafts and core drilling. On July 1, 1933, the Idaho-Maryland Mines Company leased the Brunswick Mine from the Idaho Consolidated Mines, Inc. for five years.

By 1934, the underground workings of the Idaho-Maryland Mine extended more than 8,000 feet from the main shaft. To supply better ventilation and another exit, another shaft was created closer to the underground operations. The location for the shaft was near the intersection of Brunswick and Idaho Maryland Roads, which proved problematic from a geological standpoint. In order to operate a conventional shaft at that location would have required a vast amount of timber and constant upkeep. The shaft would not need to hoist ore or waste rock, so they tried using a 60-inch-diameter experimental, single compartment, core drill. With the use of the drill, the second shaft, called the “Round Hole” shaft, was advanced 173 feet in 1934.

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