The Clark Gruber Mountain $20, has been considered a key to the pioneer gold series since the early 20th century. Today, there are only 15 examples encapsulated at either of the third- party grading services, and a trio of genuine, ungradable examples are known. There are three uncirculated Mountain $20s in private hands, and any lustrous, original coin would qualify for the condition census. In 2006, numismatists Andy Lustig, Ron Karp, and David J. McCarthy discovered a proof striking of the Mountain $20 that apparently traced its provenance back to Emanuel Henry Gruber.
| Country | United States of America |
| Year | 1860 |
| Serie | Clark |
| Denomination | G$20 |
| Mint | Denver, Colorado |