Pausanias' Description of Greece [5.7.6] tells us that "the most learned antiquaries of Elis say that Cronus was the first king of heaven, and that in his honor a temple was built in Olympia by the men of that age, who were named the Golden Race." Is there any archaeological support for this, other than the name of the Hill of Kronos? Google searches and a read of several books on the subject has failed to reveal anything to me as of yet.
Pausanias 6.20.1 is more specific that a cult of Kronos was practised on top of the Hill of Kronos, and this more specific claim finds corroboration in an earlier source, Dionysios of Halikarnassos 1.34.3.
The hill itself is a small one, 123 m high according to the New Pauly (s.v. "Cronion"), just to the north/north-east of the ancient city as shown in this satellite image. Nowadays it's covered in pine trees.
Scholia on Pindar Olympian 5.10 mention a report by Herodoros, who lived around 400 BCE (= New Jacoby 31 F 34; link, if you happen to have access through a research library), that there were six altars to the twelve Olympians at Olympia, and the sixth was an altar to Kronos and Rhea. Herodoros explains that according to one variant of the foundation legend for the Olympia festival, these altars were founded by Herakles (probably a local Elean variant of Herakles, who was called Herakles Daktylos or "Herakles the finger-high").
There isn't any archaeological evidence to support any of these references. However, the combined testimony of Pausanias, Dionysios, and Herodoros is plenty to support a cult of some kind. A hilltop cult sounds like it could (speculatively) be a very very early one - though the Hill of Kronos is no mountain.