The Oak mine was a lode gold mine located one mile northeast of Omo Ranch. I was active in 1894 when a one to four-foot vein of gold-bearing quartz in granite was developed by a two adits, one 400 feet in length and the other 150 feet in length. The ore was treated on-site in a five-stamp mill. Later three different mines at this location: the Black Oak, Crown Point and August, would become the Oak Consolidated mine. Together they totaled 30.92 acres.
Another Oak mine was a placer gold mine located one-half mile north of Omo Ranch.
The Oakland (formerly McNulty) mine was a lode gold mine about four miles south of the town of El Dorado on the Mother Lode. By 1890 the vein, which has an average thickness of four and one-half feet, had been opened to a depth of 450 feet. At that time work was in progress to continue down an additional 350 feet. The ore was crushed with a ten stamp mill. Several Pelton (water) wheels were used to provide power for driving and pumping.
The Oakland Consolidated mine was a lode gold mine consisting of two adjacent locations, the Oakland and Machine, one-half mile northwest of Greenwood on the western branch of the Mother Lode
The O’Brien (S-Bend) mine was a chromite mine located two miles north of Coloma, west of Perry Creek (not to be confused with the Perry Creek near Fair Play, in the southern part of the county). It was active in 1918, during World War I, and again in 1942, during World War II, when there was a critical need for chromium. In 1918 several hundred tons of ore were produced and in 1942, over 3000 tons was produced and then treated at the Volo Mill, west of Placerville. The mine was developed by two adits and a “glory hole” (large open pit created by mining from the bottom).
The O’Brien and Tulley mine was a placer gold mine adjacent to the town of Newtown.
The Ogle mine was a chromite mine one mile south of Volcanoville. Like many of El Dorado County’s chromite mines it was active for one year, 1917, when 47 tons of 45 percent ore was produced from an open cut.
A second Ogle mine was a placer gold mine one-half mile northeast of Volcanoville, a short distance away from the previous one .
One mile east (north in some descriptions) of Greenwood on 18 acres of the western branch of the Mother Lode was the Ohio (Eagle) mine, a lode gold mine. It was active in 1894-96 when a four-foot wide vein of gold-bearing quartz was developed by a 250-foot inclined shaft.
Another lode gold mine with the name the Ohio mine was located one and one-half miles southwest of Grizzly Flat. It was active prior to 1894 when a four-foot wide vein of gold-bearing quartz was developed by a 135-foot vertical shaft and an inclined shaft of unknown depth. The ore averaged 12 dollars of gold per ton.
A third Ohio mine was a placer gold mine three miles south of Coloma in Gold Hill.
The Ohio Tunnel Co. operated a placer gold mine on 60 acres one and one-half miles north of Smith Flat.
The Old Abe mine was a lode gold mine three miles south of the town of El Dorado on the Mother Lode.
The Old Empire mine was a placer gold mine on 30.12 acres at Henry’s Diggings, one and one-half miles north of Omo Ranch. Nothing more is known about it.
The Old German mine was a placer gold mine one mile north of Indian Diggings.
The Old Gold mine was a lode gold claim one-half mine north of Greenwood on the west branch of the Mother Lode.
The Old Harmon mine, a part of the Harmon Group of gold mines, was a lode gold mine in the northern part of Placerville.
The Old Henderson and Fryer mine was a placer gold mine on 80 acres one and one-half miles north of Smith Flat.
The Old Hickory mine was a lode gold mine one mile south of Kelsey on 16.69 acres of the Mother Lode.
The Old Jasper mine was a lode gold mine nine miles northwest of Shingle Springs. It was active prior to 1896 when two parallel veins of gold-bearing quartz were developed by a 200-foot drift adit and an inclined shaft.
The Old Judge mine was a lode gold mine on 40 acres of the Mother Lode, one and one-half miles north of Kelsey, near Spanish Flat.
The Old Moore mine was a lode gold mine three miles north of Cool in a somewhat isolated location with three other mines.
The Old Quartz mine was a lode gold mine two miles south of the town of El Dorado on the Mother Lode.
The Old Wheeler mine was a placer gold mine on 80 acres adjacent in Grizzly Flat.
The Olds mine was a lode gold mile on 10.95 acres of the Mother Lode, one and one-half miles south of the town of El Dorado.
The Olive mine was a lode gold mine on 40 acres of the western branch of the Mother Lode at Greenwood.
The Oliver mine was a lode gold mine one-half mile north of Greenwood on 20.40 acres of the western branch of the Mother Lode.
The Olsen and Baxter mine was a placer gold mine on 40 acres one mile east of Rescue near the intersection of Green Valley and Lotus roads.
The Olsen and Donaldson mine was a placer gold mine on 60 acres one-half mile southwest of Camino.
The Omo mine was a lode gold mine located one mile northeast of Omo Ranch. A one and one-half to three-foot wide vein of gold-bearing quartz was developed by a 150-foot adit and a 64-foot shaft. The ore was treated in a 125-foot flume with riffles made of poles.
The One Spot (Sailor Jack) mine was a placer gold, drift mine one mile south of Camino. It was active in the “early days”, when $40,000 of gold was produced, and reactivated in 1934-38. Two channels of ancient routes of the South Fork of the American River, one above the other, were developed by a 500-foot adit with drifts and raises. The mined gravel yielded up to $8 per cubic yard.
One mile north of Placerville was the One to Sixteen and Vulture mine. Nothing more is known about it.
The Onion Creek mine was an isolated placer gold mine on 160 acres 17 miles east of Georgetown, nine miles north of Pollock Pines and two miles east of Lookout Mountain. Located on Onion Creek, a tributary of Silver Creek, it is the most northeastern mine on the western slope of El Dorado County. Union Valley was at one time known as Onion Valley
The Ontario lodes mine was located on 26.086 acres of the Mother Lode, one mile southeast of Nashville.
The Ophir Quartz mine was a lode gold mine on 13.7 acres of the Mother Lode, two miles south of the townsite of El Dorado. The fourteen inch wide vein, with numerous stringers, was developed by an adit and a shaft, following the vein for 98 feet. The ore, some of which was high-grade, was crushed on-site in a two-stamp mill.
The Oregon mine was a lode gold mine on the Mother Lode one-half mile south of Placerville.
The Oregon Hill and Columbia Tunnel mine was a placer gold mine on 29.38 acres one-half mile south of Placerville, adjacent to a large group of lode gold mines along the Mother Lode.
The Ori mine was a placer gold mine on 20 acres one mile west of Gold Hill on the south side of Thompson Hill.
A Placerville company known as the Orloma Company, operated a one and one-quarter cubic yard dragline dredge and a dry-land washing plant on Indian Creek during 1941-42.
The Oro Fino mine was located on the Mother Lode, one mile south of Garden Valley. From 1925-26 and in 1930, a four-foot vein of gold-bearing quartz was mined by way of an 80-foot inclined shaft. The ore, some of which was high-grade, was treated at Frog Pond mill.
A second Oro Fino mine, often referred to as the Oro Fino-Big Canyon mine was a lode gold mine four miles south of Shingle Springs in Big Canyon.
A third Oro Fino mine shows up as being five miles south of Diamond Springs on the Mother Lode. It may be the same mine as described above. By 1900 a vein 40 feet in width had been followed by a vertical shaft 200 feet deep which then turned at an angle of 40 degrees and then continued to a depth of 540 feet, still on the vein. A 30 stamp mill processed 85 tons of ore a day, producing about one-third free gold. Gold sulfides were processed in a chlorination plant at the rate of about four tons a day. The rock at this site was considered to be extremely hard and all work had to be done using air powered drills and “Judson No. 1″ powder. When the mine was visited by the State Mineralogist in 1900 it had been shut down.
The Oro Flam (Oriflamme) mine was a lode gold mine on 20 acres of the Mother Lode, one mile southeast of Diamond Springs. Here a vein of gold-bearing quartz, varying in width from one to ten feet, was developed by a 350-foot adit and a 40-foot shaft.
One mile south of Garden Valley, on the Mother Lode, was a lode gold mine known as the Oronogo mine. It was active from 1953-55 with only a small gold output. Here, two parallel veins of gold-bearing quartz were developed by a 90-foot inclined shaft with a 20-foot drift at the 90-foot level. If you analyze the name you will see that it is oro (gold in Spanish) and no go.
The Orum (Woodland) mine was a lode gold mine on the Mother Lode three miles southeast of the townsite of El Dorado. It was active in 1914 when a one-foot vein of gold-bearing quartz as developed by a 200-foot vertical shaft with levels at 100 and 150 feet. The ore was treated in a five-stamp mill and concentrated on a Wilfley table. It was operated by the Orum Mining and Development Co.
The Overlook mine was a lode gold claim four miles northwest of Rescue, north of Deer Valley Road.
The O. W. Bowles mine was a placer claim one-half mile north of the town of Newtown.
