The Finger Lakes are glacier scoured U-shaped valleys that are now filled with ground water because the ends of the valleys are dammed.
(U-shaped valleys; are filled; with ground water; because the ends of the valleys are dammed; T:now) (the ends of the valleys; are dammed; )
U-shaped valleys the ends of the valleys
are filled are dammed
with ground water because the ends of the valleys are dammed T:now