When the world's favourite theme park opened 40 years ago, mules bit the guests and horses bolted. By Edward Helmore
Down Highway Five, 27 miles from Los Angeles towards Santa Ana, lies "The Happiest Place on Earth". You would not know it from its semi- industrial surroundings. However, once you have spotted the Matterhorn Mountain and passed though an enormous pink portal, you are in Disneyland - the park that changed the world.

On 17 July 1955, a day Walt Disney would later refer to as "Black Sunday", it opened for business. Besides 30,000 guests and a crush of gatecrashers, Disney hosted a broadcast of the event across the nation - and the whole thing nearly degenerated into chaos. Women's high heels stuck in the still-soft asphalt, the fountains did not work, there were not enough loos and Fantasyland had to be closed down because of a gas leak.

Despite this, 1 million people visited in the first seven weeks. "People were intrigued because it had never been done before," says Dave Smith, head archivist at Disney Studios. There were 18 rides; Fantasyland had "dark rides" which passed through tableaux relating to an animated film. There was a carousel, a Dumbo ride on which visitors did as Dumbo does and flew about, and in Frontierland there were horses and mules. "The mules were skittish, they bit the guests and refused to move," says Smith, "and the horses would get spooked by the train's whistle and bolt off with the stagecoach."

Disney had sought advice from amusement parks on Coney Island. Thrill ride operators told him that to spend more than $50,000 on any attraction was folly, advised him not to pay anything extra to keep the place clean, and to employ the usual fairground pickpockets to staff it, not clean- cut college types. Now, Disney's three-dimensional cartoon seems as natural as it was once revolutionary. Too revolutionary for investors: initially Disney had to put up the money himself. "I could not convince the financiers Disneyland was feasible," he later said. "Dreams have too little collateral."

Since Mickey and Minnie Mouse opened this mother of all theme parks 40 years ago, 350 million people have entered Disney's fantasy. They come to dance with Snow White, spin in a teacup, sing with a lion, cuddle a country bear, flee a fire-breathing gorgon in the Temple of the Forbidden Eye. The most popular ride, which opened in March, is the Indiana Jones Adventure, which cost $100m to build. "Hop in a troop transport for a death-defying encounter with snapping cobras, poisonous darts and a 50-ton ball of granite," reads a flyer for the three-minute thrill. It is undeniably impressive but comes with a snag: a three-hour queue.

To alleviate queue boredom, there are distractions. In the case of the Indiana Jones Adventure, visitors pass through a bazaar, down a tunnel, and up into a temple where they are encouraged to decipher the codices on the walls and, of course, to browse in stores for jungle accessories such as toy bullwhips and rubber snakes.

In between all the merchandising, the signs of age are there to see; the monorail, that false prediction of 21st-century mobility, creaks its way around the perimeter; Tomorrowland definitely looks like yesterday, with a huge model of an Apollo-era rocket and a schmaltzy song-and dance routine.

The only area with anything actually living in it is the petting barnyard at Big Thunder Ranch, where miniature ponies and docile Spanish goats are almost ignored by the high-summer crush. Like all things Disney, real life is quickly masked. A student in a cowgirl costume follows the animals with a scoop for when they thoughtlessly defecate. Disney clearly learnt from those mules.

The most convenient airport for Disneyland is Santa Ana/Orange County. Unijet (01444 458611) has flights from Gatwick on Northwest via Detroit for pounds 570 including tax. Bon Voyage (01703 330332) has a fare to Los Angeles of pounds 471 on TWA via St Louis.

Admission to Disneyland for one day costs $33 (about pounds 21). An annual passport for $199 (pounds 127) allows admission 365 days a year.