According to this article, the Colorado Libertarian Party state convention of March 20 was fairly closely divided between two candidates for the party’s nomination for the U.S. Senate. So, under a 2007 election law, there will be a primary for the party to choose its Senate nominee.
Before 2007, primaries were reserved for parties that had polled 10% for Governor. Other ballot-qualified parties were to nominate entirely by convention. But the 2007 change said that even qualified minor parties should have a primary, when their state conventions were fairly closely divided for one particular nomination.
The 2010 Libertarian primary for U.S. Senate will be the first statewide primary for a party, other than the Democratic and Republican Parties, in Colorado, since 1916, when the Progressive Party had its own primary.
The 2010 Colorado primaries are on August 12. There were 9,489 registered Libertarians in Colorado in October 2008. One of the U.S. Senate candidates is Macyln Stringer; see his web page here. The other is John Finger; see his page here.