After months of preparation, a massive boulder has begun its 169-kilometer journey to the Los Angeles County Museum of Art. The 340-ton chunk of granite that acclaimed earth artist Michael Heizer selected to be the centerpiece of his latest creation left a dusty rock quarry in Riverside late Tuesday. The boulder will make a circuitous journey through nearly two dozen Southern California cities to the museum\'s backyard, where it is to become the focal point of Heizer\'s \"Levitated Mass.\" The artist plans to have the rock placed over a 456-foot (139-meter)-long trench in such a way that when museum visitors walk underneath it will appear to be floating in the air above them. But first it has to get to LA from Riverside\'s rural Jurupa Valley, where Heizer came across it six years ago and, as the story goes, said, \"That\'s the one.\" Dozens of people were on hand to bid farewell to the rock. \"People were coming and going all day,\" museum spokeswoman Miranda Carroll said. She said the quarry even hosted a barbecue Tuesday night for museum staff and others involved with the move. Museum officials say the reclusive artist, who has spent much of the past 40 years building \"City,\" a Mount Rushmore-sized project near his home in the central Nevada desert, envisioned \"Levitated Mass\" even before that. But he couldn\'t really proceed until he found the right rock. What he found was two stories high, teardrop-shaped and so heavy and bulky it took a specially built flatbed trailer the length of a football field to transport it. The trailer, equipped with 44 axels, built to hold at least a million pounds (450,000 kg) and powered by 550- to 650-horsepower engines in the front and back, will be accompanied by as many as 60 people who will clear a path for the rock and make sure it doesn\'t smash into anything going around turns. It will travel no faster than 8 to 13 km per hour and only late at night and in the early morning. The trip is expected to take 11 days, with the rock scheduled to roll up to the museum\'s back door sometime before dawn on March 10. The curious can follow the rock\'s progress on Twitter or through the museum\'s website and blog. \"We\'re going to keep everybody updated as to where it\'s parked each day,\" said Carroll. It is a journey that has been delayed repeatedly over the past six months as 22 cities, from Riverside to Long Beach, have had to agree to let it roll through their communities. Many were wary, especially given that officials say it is likely the largest rock to be moved from Point A to Point B since the days when the ancient Egyptians were building the pyramid.