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Picket Post Mansion

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Castle on the Rocks
1923–1929, William Boyce Thompson; Jack Davey, contractor. Near milepost 223 on U.S. 60.
  • (Photograph by Heather McMahon)

The dramatically situated Picket Post Mansion was the winter estate of Boyce Thompson Arboretum founder William Boyce Thompson (1869–1930).

Located on a high ledge above the Arboretum, the so-called “Castle on the Rocks” is oriented towards the eponymous Picketpost Mountain to the south. Thompson desired a residence close to his Magma Mine in the desert town of Superior, but the land he chose lay within Arizona’s Crook National Forest (now known as Tonto National Forest), necessitating that he acquire a permit from the United States Forest Service. He later made an exchange with the Forest Service for land he owned in northern Arizona to acquire the property outright.

Thompson designed the mansion, with the assistance of draftsman at his mine who completed the working drawings, reputedly modeling it after a cliffside monastery in Greece. Built in phases between 1923 and 1929 by local contractor Jack Davey, the 26-room mansion originally consisted of three separate structures partially built into the top of the crag: the extant two-story Main House; an extant small residence for Thompson’s wife Gertrude to its east; and Thompson’s now destroyed three-story private retreat, the Cliff House, to the south. The buildings’ planar walls pierced by large thermae windows, red-tile eaves extending from the low-slung roof, and the Cliff House’s tall rectangular water tower lent the estate a Mediterranean Revival appearance. Thompson filled the interiors with antique furniture and artwork collected during European cruises. The Main House was the first section completed. It is a red brick and stucco building with an enclosed veranda wrapping around three sides of the second floor. Its first floor contained a kitchen while the second story housed the principal living spaces, including a dining room, library, sunroom, and bedrooms accessible from both the central portion of the house and the veranda. The Cliff House, like Gertrude Thompson’s house, was built of wood frame construction finished with stucco; it contained Thompson’s private suite on its third floor, his nurses’ quarters below, and a furnace on the ground floor that maintained a constant 72 degrees in his quarters. In 1929, Thompson (confined to a wheelchair after a 1925 stroke) installed an elevator in the Cliff House that allowed him to access the roof and an adjacent rock promontory, and to descend to a path around the west side of the mansion that reached the Arboretum via connecting trails.

In 1928, Thompson donated the Picket Post Mansion and the surrounding property to the Arboretum. However, the cost of maintaining the underused mansion was excessive and the Arboretum sold it in 1946. In subsequent years, the mansion went through several changes of ownership and a number of renovations, serving for a time as a bed and breakfast. In 1953, a fire destroyed the Cliff House with its distinctive water tower. In 2008, Arizona State Parks purchased the surviving 7,287-square-foot portion of the mansion (containing the 6,402-square-foot Main House and the 885-square-foot Gertrude Thompson House), reuniting it with the Arboretum, and opened it for occasional public tours to help raise funds for its eventual restoration and operation.


“Boyce Thompson Southwestern Arboretum State Park.” Arizona State Parks. Accessed March 7, 2015.

Boyce Thompson Southwestern Arboretum, Inc.: Purpose, History, Dedication. Superior, AZ: Boyce Thompson Southwestern Arboretum, 1930.

Erickson, Helen, and Gina Chorover. “Historic American Landscapes Survey (HALS): Boyce Thompson Southwestern Arboretum.” Paper presented at the Arizona Historic Preservation Conference, Prescott, Arizona, June 2012.

Erickson, Helen, Gina Chorover, Rebecca Field, Allison Kennedy, and Sylvia Lee, “Boyce Thompson Arboretum,” Pinal County, Arizona. Historic American Landscapes Survey, National Park Service, U.S. Department of the Interior, 2012. Prints and Photographs Division, Library of Congress, HALS AZ-7.

“Picket Post Mansion Tours.” Boyce Thompson Arboretum. Accessed September 13, 2017.

Wilson, Marjorie, “Boyce Thompson Southwestern Arboretum,” Pinal County, Arizona. National Register of Historic Places Registration Form, 1975. National Park Service, U.S. Department of the Interior, Washington, D.C.

Writing Credits

Heather N. McMahon
R. Brooks Jeffery
Jason Tippeconnic Fox



  • 1923


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Heather N. McMahon, "Picket Post Mansion", [Superior, Arizona], SAH Archipedia, eds. Gabrielle Esperdy and Karen Kingsley, Charlottesville: UVaP, 2012—,

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