All-Star Comics #51

Several mysterious events in Civic City spur the JSA to meet with Army officials, and are mystified by the uncanny predictions of a scientist named Crillon. They attend a meeting where Crillon is speaking about a race of Diamond People who live beneath the surface of the Earth whom he believes are responsible for the events happening re the Bottomless Lake and Old Reliable Geyser, and that a major catastrophe may occur if people do not act soon. When Crillon and a Mr. Exnam suddenly disappear at the meeting and the JSA reads the scientist's notebook, they decide to act.