Dear Mr. Crosby,
Thank you for posting your request on History Hub!
We suggest contacting the National Archives at Seattle, as they hold the records direct from the Chemawa School. Their email address is firstname.lastname@example.org. The records for the master plan plat may also be in the possession of NARA’s Cartographic Unit. Please contact the National Archives at College Park - Cartographic (RDSC) via email at email@example.com.
Additionally, it is possible a local institution may have the records you seek, so we suggest focusing your search within the local area, as well.
We hope this is helpful! Best of luck with your research!
[Information provided by Cody White, Subject Matter Expert]