Hardpan is a common name for a compaction layer below ground that can be caused from plowing, driving over the area, etc.
Basically it is as the name implies just like a "hard pan".
Hardpan is found in the A Horizon.
A playa
Sandy, sandy loam. Regosol. gypsic or calcic B horizon hardpan typical of the soil.
Caliche soil is a result of aged desert soils. As the soil ages they tend to form a calcium carbonate-rich hardpan horizon.
Nothing it just wet. Leeching may occur which means the soil looses it's nutrients and a hardpan forms.
It's not 100% impermeable, but it is hard enough that it allows very little water to pass through. "Hardpan" is a word farmers use to indicate a layer of very compacted soil beneath the topsoil layer, frequently caused by large farm equipment, and is otherwise referred to as "plowpan." It is frequently a hard enough layer that crop roots are unable to pass through as they grow, even though meristematic (root tip) tissue can exert hundreds of pounds per square inch of force to try to break through. If the crops are unable to reach water and nutrients due to relatively impermeable soil, the crop will not be as vigorous or yield as well as it could.
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 2 words with the pattern -A-DP--. That is, seven letter words with 2nd letter A and 4th letter D and 5th letter P. In alphabetical order, they are: hardpan sandpit
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 3 words with the pattern ---DPA-. That is, seven letter words with 4th letter D and 5th letter P and 6th letter A. In alphabetical order, they are: deadpan hardpan skidpan
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 1 words with the pattern --RDP--. That is, seven letter words with 3rd letter R and 4th letter D and 5th letter P. In alphabetical order, they are: hardpan
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 4 words with the pattern --R-PA-. That is, seven letter words with 3rd letter R and 5th letter P and 6th letter A. In alphabetical order, they are: carapax firepan forepaw hardpan
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 4 words with the pattern H---PA-. That is, seven letter words with 1st letter H and 5th letter P and 6th letter A. In alphabetical order, they are: hardpan helipad hutzpah hutzpas
According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 8 words with the pattern -A--PA-. That is, seven letter words with 2nd letter A and 5th letter P and 6th letter A. In alphabetical order, they are: backpay carapax catapan catspaw hardpan palapas saltpan talipat