Rewards are buried and can be identified by highlighting their locations. To dig, tap on the reward, then tap the "dig" button that appears. This will require one shovel. Buried rewards next to already dug or claimed rewards are highlighted. The price to dig is always one shovel.

How do I earn shovels?

Shovels can be obtained from various sources, including the main game, limited-time quests (each quest grants at least one shovel), new types of rocks, seasonal events, and weekday and weekend events.