Pierce Mill and the Art Barn
When Superintendent Finnan advocated renovation of Klingle House in March 1934, he mentioned Pierce Mill as another park structure deserving attention. The cost of restoring it as an operating mill would be "almost negative," he wrote. Secretary Ickes was intrigued by the idea. "[Finnan's] memorandum persuades me that we ought to consider restoring not only the Mansion with a view toward preserving it as a monument, but the old mill as well," he wrote Director Cammerer. "How much would this cost?" 
Thomas T. Waterman and Malcolm Kirkpatrick, an architect and landscape architect in the Service's Branch of Plans and Design, prepared plans and estimates, and Cammerer responded in May that the mill restoration would cost $19,250. The Service had already applied for the money as a public works allotment, he told Ickes, and could start work promptly if the project were approved. Perhaps expedited by Ickes' other role as public works administrator, approval was soon forthcoming. In November the frame porch on the upstream side of the mill that had been used by the teahouse concession was removed to clear the way for reconstruction of the water wheel and mill race. The Fitz Water Wheel Company of Hanover, Pennsylvania, prepared working drawings under a $500 contract and restored the milling machinery for $7,465. It was powered by an undershot wheel, less efficient than an overshot wheel but not requiring the high elevation of water supply needed for the latter. The project was completed in March 1936 at a total cost of $26,614. 
Mill operation began on October 27, 1936, under the supervision of Robert A. Little, a veteran miller employed by the Welfare and Recreational Association of Public Buildings and Grounds. The meal went to the cafeterias run by the association in government buildings and was sold to the public at the mill. To preclude charges of unfair competition with private enterprise, the association was careful to advertise its sales prices as "higher than in the stores." 
The mill ran sporadically and was never a high-volume business. Machinery breakdowns, fluctuations in the water supply, and the unavailability of trained millwrights caused operation to cease in 1958. Interest revived in the next decade, and in 1967 Blaine E. Cliver, a Service architect, recommended measures to resume operation. The water wheel and shaft had decayed beyond repair, and Cliver found the undershot design of dubious authenticity. On his advice the machinery was redone with an overshot wheel.  Because of the difficulty of getting Rock Creek water at a level high enough to power it, municipal water was piped to a short exposed race above the wheel.
The mill ran again in July 1970. Miller Robert Batte tended it, aided and succeeded by Brian Gregorie. A tropical storm in September 1975 damaged the machinery and forced another suspension of operations. Repairs were made, but operation continued on a sporadic rather than steady basis. For most visitors on most occasions, the picturesque appearance of the mill and the interpretive exhibits and leaflets explaining its operation had to suffice. At this writing the park was reactivating the mill for regular service, so its future may be livelier.
Two other historic structures nearby enhance the setting of Pierce Mill. The earliest of Isaac Pierce's buildings remaining is a blue granite springhouse, built in 1801 and now straddled by the divided lanes of Tilden Street. Directly west of the mill is one of several barns built by Pierce. Predating the mill, it has a frame front and sides of blue granite, which like that for the springhouse was quarried along Broad Branch.
In May 1971 the barn was reincarnated as the Art Barn, displaying art exhibits under an agreement with the Associates of Artists Equity. This arrangement received special legal sanction in 1984, when Congress authorized the secretary of the Interior to negotiate a five-year contract with the Art Barn Association (successor to the Associates of Artists Equity).  Using the barn in this manner, however distant from its historical function, would help insure its preservation.