A rock at the ALMA site

Detail of one of the reddish conglomerate-type rocks observed around the ALMA site. Around and above the ALMA Operations Support Facility (OSF), located on the road to Chajnantor, at 2900 m altitude, many grooves and gullies produced by the water flow, which was probably more abundant in the past, can be observed. The grey-reddish colour characterises the volcanic terrain, formed by pyroclastic sediments. ALMA, the Atacama Large Millimeter/submillimeter Array, is the largest astronomical project in existence.