Modern Comics#98(1950)

The adjacent nations of Huanec and Galardo collaborate on a tunneling project, through the extremely steep mountains that separate their countries, but construction is thwarted by an inner stratum of rock that defies their efforts to pierce it, so they call in the Blackhawk Squadron for help. Using a powerful new explosive invented by Chop Chop, the Blackhawks are able to penetrate this rock. The tunnel laborers from Huanec have got some superstitious and xenophobic doubts about the wisdom of this project anyway, and there's some trouble, after which the Blackhawks are in charge of the project, and doing almost all of the work. Blackhawk gets head-konked and kidnapped by some robed hooded torch-carriers, and it turns out that a big part of the mountain range is hollow, and illuminated by secret openings in the mountain valleys above. The hollow mountain contains a lake, surrounding an island, with three large golden step-pyramids on it. The long-vanished people who built all this were the ancestors of the Huanec and Galardo peoples. One of the main mining engineers in charge of the tunnel project, is secretly leading a gang getting ready to loot these structures, and some of the mutinous laborers are in it with them. Blackhawk is rescued by the timely intervention of his team, who blast their way through the triply-hard rock and fisticuff their way thru a riotous melee. The ringleader, Maztla, is caught and exposed and arrested. And at length, the tunnel is completed, commerce and diplomacy begin between Galardo and Huanec.