Complex sentence: The river is approximately 83 miles (125 km) in length, and it drains a fertile farming region called the Tualatin Valley southwest and west of Portland at the northwest corner of the Willamette Valley.
Split into simpler sentences: The river is approximately 83 miles (125 km) in length. It drains a fertile farming region called the Tualatin Valley southwest and west of Portland at the northwest corner of the Willamette Valley.