"dense, low shrub thicket," 1850, American English, from Spanish chaparro "evergreen oak," perhaps from Basque txapar "little thicket," diminutive of sapar "heath, thicket."
In Spain, a chaparral is a bush of a species of oak. The termination al signifies a place abounding in; as, chaparral, a place of oak-bushes, almendral, an almond orchard; parral, a vineyard; cafetal, a coffee plantation, etc., etc.
This word, chaparral, has been introduced into the language since our acquisition of Texas and New Mexico, where these bushes abound. It is a series of thickets, of various sizes, from one hundred yards to a mile through, with bushes and briars, all covered with thorns, and so closely entwined together as almost to prevent the passage of any thing larger than a wolf or hare. [John Russell Bartlett, "Dictionary of Americanisms," 1859]
1844, American English, short for chaparejos, from Mexican Spanish chaparreras, leather overalls worn to protect riders' legs from the chaparro (see chaparral).