From Rebel Dawn by AC Crispin:
"Even Wookies never went down all the way to Kashyyk's surface. There were rumored to be night-crawlers down there that feasted on the blood and spirits of their victims. It was said that the spirits of those who had not honored their debts sank down to the surface, and prowled there, ready and waiting to trap and kill anyone foolish enough to come near them.
There were reputedly seven levels of distinct ecology on Kashyyk, with the seventh level being the topmost tree branches. Normally, not even the bravest Wookies ever descended below the fourth level, and even Wookie legend did not speculate on what lay belowthat. No one that Chewbacca had ever known had walked on the actual surface of his world. The bottom-most levels of Kashykk were a mystery ... and would likely remain so."
And in Timothy Zahn's Heir To The Empire trilogy there's mention of Leia suffering extreme vertigo when she peers over the edge of a platform because she can't see the ground of Kashyyk.
So how come there was a beach? How come there was sand? Normally it wouldn't bug me but Lucas exerts such control over the books that you'd think he'd maybe know about something as basic as that! Or maybe he just decided it was worth pissing off the fans of the books in order to have the cool submersible fighter thingies.
That said - I did like it. It's not and never will be a classic, I think he managed to pull it out of the fire - but it's badly burned.