Historical preservation and stabilization at Tumacácori is a never-ending task.  Over 2,000 man-hours per year are required to maintain the authenticity and safety of the ruins.  In the preservation process, the highly skilled preservation experts use only historically accurate building materials, such as local clay, silt and gravel and limestone plaster.

Left to stand against the elements and vandals, Tumacácori mission deteriorated.  Treasure hunters convinced of finding "Jesuit" gold continued to dig and redig in and around the mission.  Without efforts to preserve this monument of early history, Tumacácori would probably be no more than a mound of earth.  The following series of photos shows how the mission has deteriorated and been preserved over the years.

The color picture below shows the church interior as it would have appeared in 1822 when it was used for the first time.  Note the differences between this photo and the next photo showing the church interior as it appeared in 1891, forty-three years after it was abandoned.
 

H.M.T. Howell, a Texan traveling to California in 1849, drew the picture below of Tumacácori one year after it was abandoned.  He also wrote the following description of the church:
 

In 1860, William Wrightson in his "Second Annual Report, Santa Rita Mining Company" described the deterioration of the roof - "The roof of the church was flat and covered with cement and tiles.  The timbers have now fallen and decayed.  The chancel was surmounted with a dome which is still in good preservation."

The photo to the right, the first known photograph of Tumacácori, was taken in 1883.  Although it does not show many of the outlying buildings, it is still possible to see the deterioration that was starting to take place thirty-five years after the church was abandoned.  The facade and entrance arch were intact except for the base of the lower right column.  Destruction had not yet occurred to the southwest top corner of the second floor of the bell tower.  The baptistry window on the lower floor of that tower, however, had been cut to ground level, giving the appearance of another entrance.  In Howell's sketch above, one can plainly see the poles protruding from the walls below the bell tower.  Those scaffolding poles are still visible in this 1883 photo.

Apparently area settlers utilized Tumacácori for non-religious purposes from mid-1861 to the 1880s.  The Santa Rita Mining Company evidently transformed the cemetery into a corral about 1860.  After the area was abandoned in mid-1861 it probably sheltered only occasional prospectors who looked for the "Jesuit mines."  Some of these men undoubtedly camped in the sacristy where they built fires as attested by the soot on that room's ceiling.  By the 1880s the cemetery again served as a corral.  Cattle from the Otero ranch were gathered in the cemetery for branding in a community roundup in 1884.  The livestock entered through the hole in the east wall just north of the sacristy.
 

Sporadic liturgical use of the mission revived in the 1880s.  In the mid-1880s a priest invited Tom Bourgeois, who lived in Douglas, Arizona, to live at Tumacácori as a caretaker.  Although he spent much of his time prospecting the area, he did help a priest perform an occasional wedding or baptism.  Bourgeois was evidently replaced in the 1890s by Pedro Calistro who then served as a self-appointed caretaker.  Calistro, an Opata Indian from the Cucurpe Valley in Sonora, converted the corridor east of the sacristy into living quarters.  Neighbors helped him clean the church.  Calistro filled a big hole high on the north wall of the sanctuary above the main altar.  He tried, but failed, to make treasure hunters stop digging in the mission.  Each Easter Calistro conducted a Semana Santa or religious festival at the mission.  These yearly celebrations continued until Calistro's death in 1929.

A drastic change had occurred in the short time between the 1883 photograph and the 1889 photograph to the right.  Vandals had destroyed the lower portions of the bottom columns and the three remaining bases on the facade.  In addition the piers and spring lines of the entrance arch were demolished, leaving a gaping hole.  Individuals had dug under the southwestern corner of the belfry as well as along the top of the second floor of the bell tower.  The baptistry window suffered further damage on its east side.

By 1899, fifty-one years after the mission at Tumacácori had been abandoned, many of the surrounding buildings were beginning to collapse.   It would be yet another nine years before it would be declared a National Monument.

William P. Blake, a geologist, returned to the mission in February of 1907.  On this occasion he noted that the choir arch was no longer in place.  Tomas Alegria, son-in-law of Carmen Mendez, thought the choir arch had collapsed in 1901.  He said a family living at the mission had hung a swing for their son from the arch, causing it to fall.  Since Blake did not note the fallen choir arch in his 1905 visit but did in 1907, it was probably the Montez family swing which caused the arch to fall some time in 1906.

This picture of the church on the right dated 1907 was taken one year before Tumacácori was made a National Monument and shows the extent to which the church had deteriorated.  Coert Dubois, a forest inspector with the Forest Service, visited the site in May 1907.  He wrote to his superiors that the mission was "rapidly falling into ruins and suffering considerably from vandalism of visitors.  Portions of the paintings in the old Chancel have been knocked off for souvenirs, and the whole of the inside of the nave is written over with the names of visitors."

By proclamation of President Theodore Roosevelt in 1908, the old mission ruins of Tumacacori were made a  National Monument.  Historians, archeologists and architects decided to preserve what remained of the adobe mission structures rather than restore and reconstruct the mission complex on conjectural information.  Stabilization efforts, under the direction of Frank Pinkley, General Superintendent of the Southwestern Monuments Group, began in 1919 by making only absolutely needed repairs - after all, they only had $400 to work with!  Cement was placed under the southwest corner of the belfry on the top of the second story of the bell tower where the whole southwestern pier threatened to fall.  The missing adobe brick at the top of the second floor of the bell tower was also replaced.  Cement and stones were placed under the east sacristy wall where treasure hunters had undermined the wall leaving almost no support for the east side of the barrel-vaulted roof.  Thirty to forty feet of the west cemetery wall and the whole east side of the church were underpinned.

After receiving additional funds from the Tucson and Nogales Chambers of Commerce and the Park Service, work continued.  Portions of the east and west cemetery walls were reconstructed and the debris was removed from the nave floor.  The entrance arch was restored and doors were hung in it.  The baptistry window was reconstructed and modern wooden shutters were put on it.

In 1921 the nave roof was replaced.  Special-sized adobe brick were made to reconstruct the nave walls to their original height.  The facade pediment was rebuilt based on an 1889 photograph.  A ball, the top third of which was original, and cross surmounted the facade.  The stairs in the bell tower from the ground level to the third floor belfry were restored.  Many small holes on the exterior walls of the mission were filled to strengthen the walls and remove traces of vandalism.  By the fall of 1921, Pinkley had finished his work.

On October 30, 1929, George Boundey, the first resident Superintendent at Tumacácori Monument, arrived.  In January 1934 the Civil Works Administration began an extensive project at Tumacácori.  The mission and cemetery foundations were excavated to permit repairs and the walls were mended.  Workmen also made repairs to the bell tower and nave roof.  The entire plaza was graded to aid in water drainage away from the base of the mission walls.  An outer wall was constructed from 27,000 adobe brick which the workmen made.  The Federal Emergency Relief Administration provided funds for the completion of the wall with local workers since the Civil Works Administration was dissolved in April of 1934.

The mission was inspected in February 1946 and found to be in a disturbing condition.  Keystone bricks in the west and south arches of the belfry were loose.  Bricks in the west arch had slipped.  They needed replacing and repointing.  Exterior plaster continued to decay.  On the west wall, pits and small holes in the surface allowed rain to enter.  Much of the original plaster on the north mission wall was loose.  The columns on the mission's facade needed attention.  Inside the mission, the bell tower steps were in need of repair.  Dale King arrived on June 4, 1946, to oversee many of the required repairs.  He and his crew worked to tastefully blend the repairs to match the weathered appearance of the church.

A number of continuing problems - leaks in the nave roof, bats and their droppings in the mission, uneven settling of the structure leading to cracks and continuous decay of the plaster coating on the walls - led to ongoing deterioration of the mission.  In 1947, workmen used cement-stabilized soil, in lieu of an adequate stabilizing and waterproofing material, to seal the broken areas of the original plaster on the mission walls, including the cemetery walls.  A new roof was also installed on the nave.

Rutherford J. Gettens, Fogg Museum of Art at Harvard University, and Charlie Steen arrived at the monument in June of 1949 to make a detailed study of the mission plaster and frescos.  They found that they interior plaster had continuously peeled and recommended that it be thoroughly cleaned and then sprayed with light vinyl acetate, a substance that they thought would fix the surfaces and prevent plaster chalking and paint fading.

It seemed no matter what method was used or what materials were used, the plaster coating on the church and walls continued to deteriorate.  In 1950 workmen used a sand-lime cement scratch coat over galvanized metal lath.  Daraweld, a high polymer resin internally plasticized, was added to the scratch mix in 1960.  All of these substances created an almost impermeable plaster which trapped accumulated water in the walls and kept it from evaporating.  Had the walls been covered with the same type of plaster that the Spanish priests used, moisture could have evaporated.

Since the early 1970s, on-going preservation maintenance of the mission church and its associated ruins has been accomplished on an annual basis by specific projects and by park maintenance staff.  Major projects were undertaken in the late 70s and early 1980s that saw the removal of the shelters over the granary and church corridor, major stabilization of the cornice on the west side of the mission church, major cleaning and preservation of the interior dome murals and reattachment of historic lime washes and plasters, and the printing of the park's Historic Structures Preservation Guide and Historic Structures Report.  These reports provided the guidance for the preservation of the mission ruins for the present and the future.

In the 1990s, Tumacácori National Monument hired its first staff position dedicated to the preservation of the park's cultural resources.  The mission ruins of Los Santos Angeles de Guevavi and San Cayetano de Calabazas were added to Tumacácori National Monument in August of 1990 thus creating Tumacácori National Historical Park.  With the addition of the new sites, preservation concerns as well as workloads have increased.  The park presently is dealing with these issues through a new Park Service program called Vanishing Treasures.  The Vanishing Treasures program deals with the preservation of ruins through a programmatic approach where park personnel are trained in several preservation strategies including documentation and treatment intervention.  In 1998, over 2500 person hours were spent in the preservation of the Franciscan church and 800 person hours on stabilization of the convento, granary, and morturary chapel.

It is obvious from the state of the mission today, that the preservation and stabilization efforts have been successful.