High-resolution resistivity profiles support photographic evidence of a narrow, linear feature east of the Emerald site, a pre-Columbian Native American (Mississippian Culture) ceremonial site in southwest Illinois. Part of the Cahokia society, the Emerald site consists of one large and eleven smaller earthen structures built on a Quaternary-aged glacial ridge. A nearly kilometer-long resistivity anomaly stretches across 3 different farm fields, crosses 2 roads and is evident in both upland and lowland parts of the site. We conclude that this feature is man-made and pre-dates historical settlement. The most likely explanation is a trail constructed to bring pilgrims to the Emerald site. We acquired ten high-resolution shallow dipole-dipole earth resistivity profiles in farm fields immediately east of Emerald Mound. Short (150 to 160 m long) lines imaging the upper 2 m of soil were aligned at approximately 100-m intervals crossing lineaments which appear on air-photos of the site. Resistivity values are typically between 10 and 35 ohm-m but increase to 200 ohm-m on the sandy ridge slope. We expect that soil compaction associated with the ancient trail will result in localized increases in resistivity. After calculating 2-D inversions, we extracted normalized resistivity values at 43 cm depth on each profile. When aligned, a narrow high-resistivity anomaly can be traced from line to line across the array of profiles within the area of one of the lineaments evident on the air photos.