A mission was much more than a church.  It had housing for the Pimas and the priest, work shops, class rooms, a cemetery, a mortuary chapel, an irrigation system, gardens, orchards, and grazing lands.  Until 1998, there were no structures or any other physical indications at Tumacácori National Historical Park that would indicate that there was an active Native American community here. Without this community, there would have been no mission since the Indians were the main focus of mission efforts.  One of the best ways to give visitors an immediate sense of a once thriving Native American community was the construction of a ki or traditional O’odham house.

The O’odham house or ki is made from the earth and native plants of the Sonoran desert.  Sturdy mesquite forms the support posts.  The wattle and daub or jacal constructed walls are mud interspersed with ocotillo and saguaro ribs.  The roof is mud and native grasses.  Outside the ki is a ramada or brush shelter that provides shade for daily activities and a mud oven for cooking.

The construction of the ki starts with four corner posts as far apart as people want the sides of their house to be.  Most are about eight feet by twelve feet.  After the posts have been set, saguaro ribs are tied between posts on both what is going to be the inside and the outside of the house.  Ocotillo branches are then stuck down between the saguaro ribs and into the ground about six inches.  These branches are put as close to each other as they can be.  When all four sides have been done with an opening left for a door on one side, adobe mud is plastered on the inside and outside of the house.  More ocotillo branches are put across the tops of the walls to start the roof.  On top of them are put branches of creosote in a thick layer.  Then, about a foot of dirt is put on top of all that.  When it rains, the dirt turns to mud.  When the mud dries, the roof has been plastered like the sides of the house.

The ramada, or vato, is made with four tree trunks set in the ground where the corners are going to be.  Saguaro ribs are tied between them on the ends and along the sides.  Ocotillo branches are then laid over the saguaro ribs to finish the rods.  A ramada is a perfect shelter for the desert since it shades its occupants from the sun but lets the breezes blow through.

The O’odham and their ancestors have lived well adapted to the desert climate for centuries.  Ki’s have been built in a special manner as protection from the desert heat.  However, with the advent of railroads in the last century and the availability of manufactured building materials and air conditioning systems fewer and fewer Ki’s were built.  Today, there are a few 20-year old ki’s in Big Fields on the O’odham reservation and one still on O’odham lands in Sonora, Mexico.

The ki at Tumacacori National Historical Park was built in 1998 by O’odham men from the San Xavier Tohono O’odham Reservation using  native materials collected through a collection permit on the nearby Nogales district of the Coronado National Forest as well as some purchased materials.  These men employed traditional ki construction techniques which were in danger of being lost to future generations.  As repairs on the ki are needed, the park plans to have O’odham men return as demonstrators.