Complex sentence: Despite steep slopes, periodic landslides, and multiple earthquake faults, many residences have been built in the Tualatin Mountains, though much the northern portion is undeveloped land within the 5,000 acre (20.23 km²) Forest Park.
Split into simpler sentences: Despite steep slopes, periodic landslides, and multiple earthquake faults, much of the range is residentially developed. Much of the northern portion is protected land within the boundaries of 5,000 acre (20.23 km²) Forest Park.