All-sky spectral imagery has been used to study the altitude distribution of OII(732--733 nm), OI(630 nm), and N2(1PG) emissions in tall auroral rays appearing at the poleward edge of the auroral oval. The OII(732--733 nm) emission layer was consistently higher than the OI(630 nm) emission layer in these structures; the peak emission altitudes were estimated to be ~380 km and ~240 km, respectively. Neither the high absolute altitude of the OII(732--733 nm) peak nor its >100 km offset from the OI(630 nm) peak are consistent with published model results, which consider electron impact on atomic oxygen as the sole source of auroral O+(2P). The present results suggest that O+(2P) may also be excited directly from ambient ionospheric O+(4S) atoms. Other contributing factors may include a significant underestimation of the rate coefficients for O+(2P) quenching, or field-aligned up-flows of ionospheric O+.