Defects in semiconductors lead to deleterious effects in electron devices, but identifying their physical sources can be difficult. An example of this in gallium nitride (GaN) high electron mobility transistors is the well-known trap state located at approximately EC-0.57 eV. This trap is strongly correlated with output power degradation and reliability issues, but despite two decades of study, its specific physical source is still unknown. To address this long-standing question, two complementary nm-resolution characterization techniques - scanning probe deep level transient spectroscopy (SP-DLTS) and electron channeling contrast imaging (ECCI) - were used to spatially map the lateral distribution of these traps and to image and characterize their relation to residual threading dislocations within NH3-MBE-grown n-type GaN. Direct comparison of the SP-DLTS and ECCI measurements on the same sample region reveals highly localized concentrations of EC-0.57 eV traps that are spatially correlated with pure edge type threading dislocations in the GaN, but not with mixed and/or screw type dislocations, indicating that the specific dislocation character is a defining factor for this particular defect level. This work demonstrates the efficacy of combining these two techniques to obtain energy-, location-, and structure-resolved characterization of defects in a functional device structure.