See the context of this sign.

The Prairie of the Mass

Rev. Pierre DeSmet (1801-1973) was born in Belgium but came to America in 1821,
joined by the Jesuit Society and began his work with the Indians. In his work,
he established 16 treaties, crossed the ocean 19 times and traveled 180,000 miles
on his errands of charity for the Indians who knew him as “The Sincerest Friend”.
On July 5, 1840, in the presence of 2,000 Indians, trappers and traders he offered
the first Holy Mass in what is now Wyoming on an alter of native stone decorated
with wild flowers. In Father DeSmet’s own words; “It was a spectacle truly moving
to the heart of a missionary that this immense family, composed of so many
different tribes should prostrate themselves in equal humility before the “Divine
Host.” The monument of the site was erected in 1925 and a commemorative Mass is offered there annually in July. On July 4, 1940, the 100th anniversary of the
first Mass, a Pontifical high mass was offered by the Most Rev. Biship McGovern
assisted by more than 30 priests and attended by about 2000 people.

Don't miss the rest of our virtual tour of Sublette County in 1908 images.