岩盤

1. Origins, structure, and basic meaning

• Structure: 岩盤 (がんばん) is a geological noun for a continuous hard layer of rock underground or exposed at the surface.
• Basic usage: 地下の岩盤の状態を調べる makes the foundation layer the object of a pre-construction survey, while 硬い岩盤が地表に出る makes exposed bedrock the subject on a trail.

2. Common pitfalls and similar expressions

• Subsurface base and surface exposure
  • 地下の岩盤 and 地表に出る岩盤 differ in location but may be the same continuous formation. The term is distinct from one loose stone.