Diane Lane wanted Viggo Mortensen to be in the film so much that she gave up part of her salary so that the production could afford him.
Diane Lane commented in an interview, "If Viggo and I convince people we're enjoying every second of that encounter [in the waterfall] we've really done our job as actors. It was freezing in that river. The water was filled with debris and cigarette butts and the rocks were covered in little worms."
Dr. Fogler's Bungalows was based on a real Catskills bungalow colony called Dr. Locker's which existed for many years in the sleepy Sullivan County hamlet of Mountaindale, NY. It was where writer Pamela Gray spent her childhood summers.
Much of the licensed music in the movie is by acts who performed at Woodstock, but two famous names associated with it actually were not there. Joni Mitchell felt she had to decline her invitation, but later composed a song ("Woodstock") about the festival. Big Brother and the Holding Company were never invited. Janis Joplin had left them the year before, and she performed there with the Kozmic Blues Band.
When Grateful Dead were invited to play at Woodstock, their manager wanted the promoters to add another act he managed; he offered them two. They tossed a coin, chose Santana, and the rest is history. There is no Santana music in this movie, but perhaps they are subtly represented by the act the promoters did NOT choose, It's a Beautiful Day, with their hit "White Bird"