The fastest way to farm Limestone
Limestone is a Rock Smash mining material found in two spots — the western cave of Rocky Ridges and the eastern island of Sparkling Skylands.
Rock Smash limestone blocks in Rocky Ridges' western cave, or on the eastern island of Sparkling Skylands once that region is open to you; both spots are dedicated limestone deposits rather than mixed ore veins, so a single sweep tends to yield a large haul without much digging around.
Limestone only matters once you've built a Concrete Mixer (which itself costs 2 Iron Ingots), since that's the only way to turn it into Concrete — load the mixer with Limestone near a water source and have a Crush-specialty Pokémon run it. Because the mixer recipe unlocks partway through Sparkling Skylands progress, there's little reason to stockpile huge amounts of Limestone before then; grab it opportunistically on ore runs and start dedicated farming once the mixer is actually built.
Related: Limestone, Concrete, Iron Ingot
Regions: Rocky Ridges, Sparkling Skylands