Sentence:  Having a layer of <WSD>caliche</WSD> at depths of 16 inches and less really puts a damper on the garden site. The <WSD>caliche</WSD> does not allow roots to penetrate it (tree roots often take 10 years to break through a caliche layer) nor does this mineral allow water to drain. 
Meaning of the word marked with <WSD> tags:  A layer of hard clay subsoil or sedimentary rock; hardpan.