Bedrock
Bedrock was a layer of solid rock that lay beneath loose deposits of rock.
In 2151, Malcolm Reed couldn't detect any basement or bedrock beneath Riaan's apothecary. (ENT: "Civilization")
In 2367, Geordi La Forge suggested that trapped men could be freed by using the USS Enterprise-D's phasers to cut a shaft through the bedrock to a storage tunnel, enabling transporters to get a lock on them. (TNG: "Legacy")