This is a spectacular Clark Gruber and Co. double struck $20 gold piece. Clark Gruber was the most respected and well known financial and banking company in the pioneer and Gold Rush days in Colorado. Clark Gruber and Co. opened a bank and mint in 1860 and became coiners, striking their own gold coins of proper weight. The denominations struck were $2 1/2, $5, $10 and $20. These pieces were accepted as currency since Clark Gruber and Co. was a well known private minting firm with an excellent reputation.
Although PCGS certified this double struck Clark Gruber $20 as EF 45, in my opinion it is closer to AU 50 since it exhibits some luster and has the detail showing. Red Book lists it in EF at $22,000 although this piece would trade for at least $30,000 as just a regular strike.
Since it is double struck with some rotation between the two strikes, it is a spectacular and rare major mint error. It would be the centerpiece of any U.S. error collection. There are 2 or 3 known Clark Gruber $20 gold pieces struck over Assay pieces, but that was done deliberately and is considered an overstrike and not a mint error.