The woman was reunited with her black poodle mix at the bottom of the 3-foot-wide pit, the (Portland) Oregonian reported.
The woman began shouting for help, and a passerby heard her and called 911.
Fire crews used a rope to pull the dog out of the pit and a ladder to rescue the woman.
Both were uninjured from the fall, which took place Tuesday night, Portland Fire and Rescue spokesman Lt. Rich Chatman said.
It was not clear how the sinkhole had formed, the Oregonian said.