Uplift eventually exposed the crystalline complex to erosion. Arkose conglomerate and mudstone of the lower Crystal Spring Formation were created from muddy debris derived from stream erosion of these uplands. A warm shallow sea spread over the area as the Amargosa aulacogen slowly subsided; thick sequences of lime-rich ooze with abundant colonies of algae called stromatolites were then laid down. Dolomite and limestone resulted, forming the middle part of the Crystal Spring Formation. The upper part was formed after silt and sand destroyed the algal mat, forming siltstone and sandstone. Laterally extensive diabase sills of molten rock later intruded above and below the carbonate rock layers; commercial grade talc was formed from thermal decay of carbonate rock at its contact with the lowest sill, which covers hundreds of square miles (many hundreds of km2). Today the formation is thick.