hardpan vs caliche

hardpan and caliche both are nouns.

Word	Noun	Adjective	Verb	Adverb
hardpan	Yes	No	No	No
caliche	Yes	No	No	No

As nouns, hardpan and caliche are synonyms defined as:

hardpan and caliche: crust or layer of hard subsoil encrusted with calcium-carbonate occurring in arid or semiarid regions

hardpan (noun)	caliche (noun)
crust or layer of hard subsoil encrusted with calcium-carbonate occurring in arid or semiarid regions	nitrate-bearing rock or gravel of the sodium nitrate deposits of Chile and Peru
	crust or layer of hard subsoil encrusted with calcium-carbonate occurring in arid or semiarid regions