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A hard, usually clay-rich layer of soil lying at or just below the ground surface, in which soil particles are cemented together by silica, iron oxide, calcium carbonate, or organic matter that has precipitated from water percolating through the soil. Hardpans do not soften when exposed to water. Also called caliche.

1.  A layer of hard subsoil or clay. Also called caliche.
2. Hard, unbroken ground.
3. A foundation; bedrock.

(Earth Sciences / Physical Geography) a hard impervious layer of clay below the soil, resistant to drainage and root growth