LEGO Power Miners was released in 2008. It features miners underground searching for crystals. The only thing stopping them is the Rock Monsters. The Rock Monsters always eat the crystals for power.
Currently this LEGO theme has 6 main sets. These main sets can be combined to make a combination model. Instructions for the combination models can be found at the LEGO website under the Power Miners page. There are other sets for this theme but these can not be combined.