Complex sentence: Tallest known living specimens today grow in southern Oregon; one in Umpqua National Forest is 77.7 m (255 ft), and another in Siskyou National Forest is 77.2 m (253.5 ft).
Split into simpler sentences: Tallest known living specimens today grow in southern Oregon. One in Umpqua National Forest is 77.7 m (255 ft) and another in Siskyou National Forest is 77.2 m (253.5 ft).