"Padre Munoz, who accoompanied Gabriel Moraga on his expedition through the
San Joaquin Valley in 1806, records in his diary
(Arch. MSB 4:1-47) on Sept. 27, 1806: 'This place is called [the place] of the
mariposas [butterflies] because of their great multitude, especially at
night and morning. ... One of the corporals of the expedition got one in his
ear, causing him considerable annoyance and no little discomfort in its
extraction.' It is, of course, not certain that the arroyo at which the
expedition camped is identical with the present Mariposa Creek. The name Las
Mariposas was given to two land grants, dated Sept. 19, 1843, and Feb. 22, 1844.
Fremont speaks in his Memoirs (p. 444) of a
Mariposa River in connection with his third expedition (1845- 46). In 1847
Fremont acquired the claim for the rancho that had been granted to Juan B.
Alvarado in 1844. He expresses his own ideas (p. 447) on the origin of the
name: 'On some of the higher ridges were fields of a poppy which, fluttering
and tremulous on its long thin stalk, suggests the idea of a butterfly settling
on a flower, and gives to this flower its name of Mariposas -- butterflies --
and the flower extends its name to the stream.' Fremont's version of the origin
of the name of the stream is hardly acceptable even without Munoz' direct
evidence. However, the Mariposa lily (Calochortus spp.) takes its name
from the California toponym. When the county (one of the original twenty-seven,
and at first including most of southern California) was created on Feb 18, 1850,
the singular form, Mariposa, was chosen. The town sprang up when gold was
discovered on Mariposa Creek in 1849; it was moved to the present site early in
1850. Mariposa Grove [Yosemite NP] was discovered by Galen
Clark and Milton Mann in May 1857 and was so named
because it was in Mariposa Co. It is mentioned as Mammoth Grove of Mariposa
in Hutchings' Illustrated California Magazine of Dec. 1858.
Mariposa Peak [Merced, San Benito, Santa Clara Cos] was apparently
named by the USGS when the Quien Sabe quadrangle was mapped in 1917-18."