As of August 4, 2015, Red Rocks Park and Mount Morrison Civilian Conservation Corps Camp have been designated as Colorado’s newest National Historic Landmark (NHL)!

This long process officially began in about 2004 at the suggestion of the Friends of Red Rocks, a nonprofit group formed in 1995 to advocate for the park. The work on the nomination has been carried out by staff and consultants of Denver Parks and Recreation and the regional office of the National Park Service (NPS), and the nomination itself has been through several revisions over the last five years; a “final” version was officially submitted to the NPS in Washington on May 1, 2014.

During the last stages of the process, many groups and individuals wrote letters of support for the designation, including Governor Hickenlooper, History Colorado, Jefferson County Commissioners, the Denver Art Museum, the Denver Mountain Parks Foundation, and Bonnie Raitt. Secretary of State Sally Jewell signed the completed nomination August 4th, bringing the effort to a successful conclusion.

Red Rocks designation, Denver Post, August 4, 2015

Red Rocks and CCC Camp up for designation, Denver Post, February 24, 2015

The outstanding architecture and landscape architecture of Red Rocks Park and Mount Morrison Civilian Conservation Corps Camp illustrate the principles and practices of New Deal-era naturalistic park design and master planning in a metropolitan park as well as the use of Civilian Conservation Corps labor to develop such a park.
—National Park Service press release.

How does this new designation differ from National Register status?

Red Rocks Park District was named to the National Register of Historic Places in 1990, along with several other Denver Mountain Parks. The National Register listing is a process for recognizing historic sites that are usually at least 50 years old, and are significant according to listing criteria, including things like their association with historic people, events, etc. Although nomination and listing on NRHP is a substantial process, nominations are handled by the state historic preservation office before involving the NPS in Washington.

National Register Fundamentals (at nps.gov)
National Register of Historic Places on Wikipedia

Colorado has more than 1400 sites, buildings, and districts listed on the National Register, but only 24 National Historic Landmarks (Civic Center included) and 14 National Natural Landmarks (Summit Lake Park is one).

Historic Landmarks are automatically listed on the NRHP, but not all NRHP sites are, or are eligible to be, historic landmarks. NHLs have national significance, as opposed to just state or regional significance.

The National Historic Landmark is a much more prestigious and exclusive designation and the nomination process is much more detailed. Although none of these designations confer protection on a property, the landmarks do involve some federal review to ensure the landmarked sites maintain the qualities that make them significant and worthy of this high honor.