"The geophysical survey did not find conclusive evidence for a mass burial, as hypothesized by local legend. However, there is one potential area within the survey block that may contain unmarked burials and should be confirmed via ground truthing. . ." — Molly Cannon, Ph.D.
Ground penetrating radar was used to visualize the surfaces throughout the area, including below ground. Magnetic gradiometry produced a dense dataset to detect small subsurface features. The use of two different instruments helped researched more accurately identify what they found.
Could the unmarked burials be Chinese workers? There's no way to know from surface surveys.