All DTV towers are in the West Hills, where most of the analog transmitters are.
These two transmit from the "2-headed" tower:
27 KOPB-DT PBS (doesn't transmit all the time)
46 KGW-DT NBC
These two share a common antenna, the orange-colored one on the tower located very close to the analog KOIN ch. 6 tower:
40 KOIN-DT CBS
43 KATU-DT ABC
30 KPTV-DT UPN Tune in if you really like screen logos.
48 KPDX-DT Fox Although they've been having off and on problems lately.
'not surprising your friend didn't know this; other than KOIN, the rest seem to be trying to do their best to keep their digital transmitters a secret.