The Rock Creek Park Commission met at the War Department on October 2, 1890, only five days after approval of the act creating it. Brig. Gen. Thomas L. Casey, Army chief of engineers, was elected chairman; the other members were Lt. Col. Henry M. Robert, engineer commissioner of the District of Columbia, Prof. Samuel P. Langley, secretary of the Smithsonian Institution, Brig. Gen. Henry V. Boynton, and R. Ross Perry. Capt. William T. Rossell, assistant to the District engineer commissioner, served as the commission's executive officer (succeeded by Capt. Gustav J. Fiebeger in 1892). 
The park commissioners took to the field later that month to view their domain. They decided that the eastern boundary should follow the alignment of 16th Street above Blagden Mill Road and that the western boundary should run along Broad Branch Road and Daniel Road (present Oregon Avenue) to the District line. On November 7 they ordered the necessary survey of the proposed park and the tracts within it that would need to be acquired. The map and schedule of assessments were ready the following spring. Because the legislation required the President to approve all payments, the commissioners called upon Benjamin Harrison at the executive mansion on April 4, 1891, and obtained his concurrence in the land valuations. 
The map and assessments schedule were filed with the District Recorder of Deeds on April 16, at which time a circular letter was sent to landowners advising them of the action and offering to purchase at the appraised values. Very few were willing to accept the sums offered. The commission reached agreement with several owners to buy tracts at higher-than-appraised prices with President Harrison's approval after the attorney general advised that this was legal. For the remaining majority of tracts the District supreme court appointed an appraisement committee, as prescribed by the legislation. Its valuations, confirmed by the court, brought the total land costs to $1,430,000--$230,000 more than the available appropriation. 
Meanwhile, recalcitrant landowners contested the condemnation of their property as unconstitutional. The court ruled against them in July 1891. Some then found previously unsuspected values in their lands. Commissioner Perry told the commission on September 26 that "the gold bearing qualities of the rock in the tracts owned by Mr. Shoemaker and Mr. Truesdell had assumed important proportions." An appraisal by an expert from the United States Mint in Philadelphia was arranged.  The commission record is silent on his findings, which presumably were unfavorable to the claimants in view of the subsequent court-approved valuation.
The valuation in excess of the appropriation required that some of the lands selected for the park be omitted. After a restudy, the commission identified tracts near the District line and along 16th Street as least vital. On April 13, 1892, the President approved purchase of the remaining lands at the set prices. Payment was given the court, which on June 21 granted possession to the commission in the name of the United States. Through agreement and condemnation, the commission acquired 1,605.976 acres in all at a total cost of $1,174,511.45 including expenses. 
There remained the business of assessing neighboring landowners based on any increase in their property values from the park. The commissioners pursued this requirement of the legislation without great enthusiasm and in the face of further opposition and litigation by affected owners. Their final determination, reported to the court in December 1898, was that the park in its unimproved state had caused no appreciable increase in property values; thus no assessments were warranted.