US 26, 3c Dull Red, Ty. III (26) tied by SAN FRANCISCO / Cal. // JUN / 5 (1861) CDS on cover to Raphael Pumpelly, Esq, Santa Rita Mining Co, Tubac, Arizona. Red docketing “San Francisco June 4, 1861…To dear Pumpelly, From Louis Janin.” Probably carried on the steamer Panama, which sailed south to Mazatlan on June 6, taken by stage from San Diego to Tucson, then by Lathrop's Buckboard Mail to Tubac, Very Fine and RARE USE TO SECEDED ARIZONA TERRITORY. Ex Birkinbine. $2,750.

Raphael Pumpelly (1837-1923) was a geologist, engineer, explorer, author, and professor at Harvard, who was associated with the Salero Mining Company, headquartered in Tubac from 1858 to 1861. Pumpelly was recruited to improve the company's performance, but constant attacks by Apaches eventually led to the company's demise, as well as the death of one of its principals, Horace C. Grosvenor. From 1866 to 1875, he was Professor of Mining Science at Harvard University.  Louis Janin (1837-1914) was born in New Orleans. He entered Yale University in 1854 but left early to travel to Europe with his brother to study languages in Dresden. He attended the Mining Academy at Freiburg until 1860. In April, he went to California with his brother Henry, where Louis took over the Enriqueta mine. In November 1861, they worked in several places before moving to Nevada, where Louis was the metallurgist of the “Mexican Mill” until October 1863. He then left for San Francisco with a 4-month tour through Sonora, Mexico, and Arizona. In 1864, he took charge of the Gould & Curry Mill at Virginia City, Nevada, and became superintendent in 1865. There is a Louis Janin from New Orleans who was a private in Company 2 of the socially prestigious Washington Light Artillery Battery of New Orleans (Confederate). He was a prisoner of war at his surrender in May 1865 in Citronella, Alabama; he was paroled May 1865 at Meridian, Mississippi. This biographical info came from https://wchsutah.org/people/louis-janin1.pdf but the wartime mining information seems in direct conflict to the military service, so it sounds like different person to me, although likely related. Up to you to determine the veracity.