From the National Park Service

The San Xavier Mission, located in the Tohono O’odham town of Wa:k, was founded by Father Kino in 1692 and was completed in 1797. It is the oldest intact European structure in Arizona, and was built by the Francisan missionary, Fr. Juan Bautista Velderrain and the O’odham people. From its delicately sculpted exterior to the ornate, painted inner church, the mission is a beautiful place rich in Arizona history.

From Wikipedia

Little is known about the people that supplied the skill and artistic talent to make this place a reality, but much of the physical labor was done by Tohono O’odham people, and it is likely the artisans were O’odham as well. In the art and sculpting, Spanish and Tohono O’odham motifs are joined into a work of art, which belongs to Arizona alone.

The mission is being actively restored, and it continues to function as both a church and a school. It is open everyday for visitors, except during mass, and serves as a gathering place for the community. For those who call Arizona home, visiting the mission is a must in my opinion, as it highlights the history and culture of the state, and for those living in and around Tucson the mission also offers a chance to take part in the St Francis Xavier Festival (held on the Friday after Easter). During which, the Tohono O’odham and Yaqui, as well as many other catholic pilgrims take part in torch lit parades and evening celebrations.

Image Belongs to A.T. Willett

When I attended the festival, it was like stepping into another, sacred world. It was dark, and firelight flickered on the fringes of my vision at all times. English took a back seat to Spanish, but the constant murmur of the crowd was overpowered by the stomped, rattled beats of dancers and the sounds of people singing in worship. The festival, while it takes place no more than 20 minutes from Tucson, is a cultural and spiritual experience, different from anything that I have ever seen in Arizona before and well worth the trip.

Official San Xavier Mission Website
National Park Service: San Xavier Mission