Chaparral and Sage Scrub ecotone is utilized by this robust perennial bunchgrass. A healthy population grows on the lower slopes of McGinty Peak. It is also seen south of Lower Otay Lake, and on hillsides west of Spring Canyon on Otay Mesa. It grows in metavolcanic soils west of Rolling Ridge Road and south of a sharp bend in Proctor Valley Road near Chula Vista.
Old reports are from Proctor Valley and Lee Valley.
Eleven specimens for Baja are found in the San Diego Natural History Museum's herbarium. It was seen growing on a hill overlooking Rodriguez Dam east of Tijuana, Mexico, intermixed with both Nassella lepida and Nassella pulchra . At this locale all three species were in seed and quite distinct, with the leaf blades of N. lepida noticeably narrower than the other two species. Also, the strongly bent awn of A. diegoensis contrasted with the shorter awn of N. lepida and the long, straight awn of N. pulchra . San Diego County Needlegrass is slowly declining on the periphery of urban expansion, and is likely to sustain more impacts in the 1990's as the southern foothills receive development pressures.