"Milos doesn't know who built the Eartshaker, but he knows that it was built at least 3000 years ago, probably by a race of evil gods with skill similar to that of gnomes or dwarves" -CM4 page 10.
3000 years ago? Well, that does place us firmly in the classic Age of Blackmoor. Another clue appeared three years later in the module DA3 City of the Gods:
Notice that humanoid figure to the right of the panel? Could it be the same figure? Granted it does look smaller than the Eartshaker, which is said to be taller than the Empire State building. However the design certainly looks similar. Giant Metallic Automatons as part of the Blackmoor mythos seem to be well established. They also appear to have been instrumental in the design of the Age of the Wolf setting, featuring such unique gigantic constructs as the Herald of Thanatos.
Recently the topic of the Earthshaker reappeared in a discussion over at the Piazza, where a project led by Chimpman has been initiated to develop a historical version of the legendary City of Urzud.