'Hardpan' definitions:

Definition of 'hardpan'

(from WordNet)
noun
Crust or layer of hard subsoil encrusted with calcium- carbonate occurring in arid or semiarid regions [syn: caliche, hardpan]

Definition of 'Hardpan'

From: GCIDE
  • Hardpan \Hard"pan`\ (h[aum]rd"p[a^]n), n. The hard substratum. Same as Hard pan, under Hard, a. [1913 Webster]