This manuscript presents the analysis of data from multiple ground- and space-based sensors in the North American region before, during, and after the 12 Oct. 2021 geomagnetic storm. The data show the formation and equatorward propagation of a density trough, which manifested within bottom-side and top-side electron density data as well as within maps of total electron content (TEC). During the recovery phase on the 13th, the equatorward edge of the trough settled at around 30° latitude and exhibited a steep density gradient. By the 14th, this sharp boundary had disappeared. Near this edge on the 13th, small-scale irregularities formed. The impact of these was observed within Global Positioning System (GPS) data as elevated rate of TEC index (ROTI) and presented as strong 35 MHz scintillations of cosmic radio sources as well as spread-F within ionograms from multiple digisonde systems. GPS and 35-MHz data demonstrated that the irregularity region was narrowly confined (≤5° wide) near the trough edge. The 35-MHz scintillation data also showed that the irregularities were moving relatively slowly at ~7 m s-1, likely toward the southeast. Density and velocity measurements demonstrate that the conditions near the trough boundary we highly favorable for the gradient drift instability (GDI) with the one-dimensional growth rate estimated to be ~0.01 s-1. Since these conditions persisted for many hours, this growth rate was more than sufficient for the GDI to be considered the primary driver of irregularity formation in this case.