The
Elephant Rocks, for which Elephant Rocks State Park is named, is a pile of residual
boulders of weathered Graniteville Granite. It is a medium- to coarse-grained,
muscovite-
biotite alkali granite that, on the average, consists of 55 percent alkali
feldspar, 40 percent
quartz, and less than 5 percent mafic minerals. The Graniteville Granite is a
pluton formed 1.4 billion years ago in the
Proterozoic by the cooling of
magma that intruded into the
volcanic strata and
country rock associated with a collapsed
caldera. Nearly vertical
fractures formed in the stone as it cooled, and uplift of the granite enhanced the fracturing. Eventually the overlying
strata were removed through
erosion, exposing the
granite pluton. Before it was exposed, groundwater
weathered the granite along fracture
joints creating
corestones of relatively solid altered granite embedded within friable
saprolite.
Surface runoff later eroded the saprolite that once surrounded the corestones and left, what are now locally called
elephant rocks as boulders perched on the ground surface. The reddish or pink granite has been quarried in this area since 1869, and two abandoned granite
quarries are within the park. These and others nearby have provided red architectural granite for buildings in states from
Massachusetts to
California, but most particularly in
St. Louis, including stone for St. Louis City Hall and the piers of the
Eads Bridge. Stones unsuitable for architectural use were made into shoebox-sized paving stones that were used on the streets of St. Louis as well as on its
wharf on the
Mississippi River. Stone quarried in the area currently is used for
mortuary monuments and is known commercially as Missouri Red monument stone. ==Activities and amenities==