caliche vs hardpan

caliche and hardpan both are nouns.

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

As nouns, caliche and hardpan are synonyms defined as:

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

caliche (noun)	hardpan (noun)
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
crust or layer of hard subsoil encrusted with calcium-carbonate occurring in arid or semiarid regions