William sent in the link https://www.yahoo.com/lifestyle/one-longest-dino-tracks-world-202823697.html … a drought in Terxas has led to the discovery of around 70 dinosaur tracks – in a dinosaur geopark [Dinosaur Valley State Park]. They were hidden beneath water and mud in the Paluxy river. Presumably, the river bed dried out. Later, it actually says the river bed was bone dry back in June. The tracks themselves were made in limestone geology – which would have been soft at the time.
The tracks were excavated rather than simply becoming visible as a result of the drought. What the drought did was provide the opportunity for a team, including volunteers, to dig out gravel, sand and dried mud, in order to get down to the limestone bedrock. A lot of dinosaur tracks have been unearthed this way, we are told.
In the UK, in Dorset for example, dinosaur tracks are also preserved in limestone geology – block cut out by quarrying.