Dear Ms Parisi,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located the series titled Unregistered Letters and Telegrams Received, 1848 - 1865 and Letters and Telegrams Received, 1849 - 1865 of the Department of the Pacific in the Records of U.S. Army Continental Commands (Record Group 393). We also located the series titled Order Book, 1855 - 1859 of the 9th Infantry in the Records of the Regular Army Mobile Units, U.S. (Record Group 391). These series may contain the letter you seek. For access to these series, please contact the National Archives at Washington, DC - Textual Reference (RDT1) via email at firstname.lastname@example.org.
In addition, we searched the Records of the Adjutant General’s Office, 1762-1917 (Record Group 94) but were unable to locate a letter from Colonel George Wright to the Department of the Pacific.
We hope this is helpful. Best of luck with your research!