From the Super Mario Wiki
Marmalade Valley is a location from Paper Mario: Color Splash. The path leading here is unlocked after getting the Yellow Mini Paint Star in Château Chanterelle, and unlocks a path leading to Kiwano Temple.
Marmalade Valley is a rocky and Western styled place where archaeological excavations are being carried out by some Toads. A Draggadon fossil can be found here, which comes to life once the orange Big Paint Star is obtained, and will be found later in Redpepper Volcano. It's also the place where the Sunset Express starts its way to Starlight Cape.
An Excavation Site Permit is required to access the excavations area, which Mario gets from the Professor. Once Mario enter the site, earthquakes happen and trap a Toad. The Bone Thing is obtained after rescuing the trapped Toad. Professor's now enormous Chain Chomp, Princess, which had caused the previous earthquakes, enters into action looking for the Bone and reveals the Draggadon fossil and the orange Mini Paint Star.
On a side note, if Mario uses his hammer before completing the level on the outside part of the construction site, he is told not to use it, because he could be hammering a million year old fossil, as said by a Toad.
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