In regions that receive about 1.3 m of rain or less, calcium carbonate will often accumulate in the lower portion of a soil profile. In fine-grained soils, such as under the prairies of the mid-western United States, the carbonate often takes the form of discrete nodules up to several centimetres in diameter. In gravelly soils such as are common in the western U.S., carbonate will begin by coating clast, and with time it will entirely plug soil voids, forming what is commonly called a caliche or more formally a calcic horizon.