I think from Angels stadium to north end is around 20-30 miles. It ends at Green river Road in Corona (91 and 71 freeways).
I haven't had problem with doing it solo.
Riverside and San Bernardnio also have a path along the Santa Ana. It currently ends at Van Buren on south end. North - i have no idea I know it goes past Waterman in SB. Long term plan is to link the two together and extend the north end to Highland