The huge pileup split the peloton about 16 miles from the finish.
Hesjedal of Canada crossed the line with his left leg bloodied, more than 13 minutes after stage winner
Danielson dropped out of the race, one of at least six to do so because of the crash. He finished eighth at the 2011 Tour and had separated his shoulder earlier in this year's race.
Hesjedal was ninth overall before the stage, 18 seconds behind leader
"I think Ryder is out," Millar said. "We'll see, but he is in a bad way."
Van Summeren reached the finish with the back of his jersey bloodied and torn and with road rash covering his buttocks.
Almost all of the Garmin riders were caught up in the pileup, the worst on this year's Tour so far.
"It was the scariest crash I've ever been in, we were doing like 70 (kph)," Millar said. "I was lucky, I think, because I was kind of in this third wave. So I started landing on guys, but then bikes were hitting me, a chain was going off."
"It was obviously a horrible crash, a lot of people got hurt real bad there - you never want to see that," he said.
Garmin sports director Allan Peiper said he had never seen a team struck by so much bad luck during the first week of cycling's showcase event.
"It's definitely a week to forget," he said. "Sometimes it just doesn't work, and this is it for us - we've got so many guys who are injured. We'll have to take stock tonight of who's still capable and who's not.
"It doesn't really matter what happened, they're all on the ground. It's just a difficult moment, we've really just lost our chances for just about everything in this Tour de France."
Garmin was embroiled this week in speculation surrounding the U.S Anti-Doping Agency investigation into