I knew I was close to the park while heading home going north. I took SW 11th Drive from Arnold and found this trail at the dead end.
Saturday, March 6, 2021
google map 
45.4506206, -122.6908294
45.45093611111111, -122.69125277777778
BOUNDARY 45.4490865, -122.6947492
BOUNDARY 45.4530947, -122.6866788
Completion of Hillsdale to Lake Oswego Trail Could Become a Reality. post