Dear Mr. Wilkinson,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located the series Records of Passenger Baggage Lists, 1871 - 1884 in the Records of the U.S. Customs Service, 1745 - 1997 (Record Group 36) that include records relating to horses during the 1870s. For access to and/or copies of these records, please contact the National Archives at College Park - Textual Reference (RDT2) via email at firstname.lastname@example.org.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDT2. We apologize for this inconvenience and appreciate your understanding and patience.
We suggest that you contact the Nevada State Archives for information about Tom Dixon and curly horse origins in Eureka, Nevada.
We hope this is helpful. Best of luck with your research!