Complex sentence: The formation is the site of the annual Panhandle Astronomy Club's Western Nebraska Star Gaze star party in June, since 2005; it was chosen because it is a good dark site, close to Bridgeport with a good view of the surrounding terrain.
Split into simpler sentences: The formation is the site of the annual Panhandle Astronomy Club's, Western Nebraska Star Gaze star party in June, since 2005. Chosen because it is a good dark site, close to Bridgeport with a nice view of the surrounding terrain.