graben
GRAH-ben
A block of the earth's crust that has dropped downward between two parallel faults, forming a valley or trough. The Rhine Graben, the East African Rift, and the Rio Grande Rift are all grabens — valleys formed not by river erosion but by the earth pulling apart and the floor falling. Death Valley is a graben. The landscape is sinking because the crust beneath it is stretching.
Etymology
German, meaning ditch, trench, or grave. The earth digs its own trench.
Notes
The counterpart is a horst — a block that remains elevated between two grabens, standing high while its neighbors drop.
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