SAN JUAN CAPISTRANO, Calif. (AP) _ Boxes of a potentially explosive mix of hazardous chemicals, found strewn along a mountain highway, were detonated today by emergency workers because they were too dangerous to move.

A 10-mile stretch of the rural Ortega Highway between Riverside and Orange counties was closed for several hours the operation. The blast had to be delayed for a time because news media helicopters were circling over the area, officials said.

The chemicals were discovered after a motorist reported a strange smell along the highway late Monday. Hazardous materials specialists, a bomb squad and 20 firefighters, all wearing breathing gear, were sent to the site about 15 miles north of San Juan Capistrano and 60 miles southeast of Los Angeles.

More than 20 different chemicals were found, including acids, corrosives and oxidizers. The materials, in containers ranging from 30-gallon cardboard drums to one-liter bottles, were strewn across the shoulder, said Orange County Fire Department spokesman Pat Antrim.

Among the chemicals was an acid-soaked box of hydrazine pellets, which are used as rocket fuel, Antrim said. The acid had leaked from another container and saturated the hydrazine, creating ''an extremely explosive situation,'' he said.

Emergency crews decided to blow up the box after stable material was removed.

''It was far too hazardous to try to remove it from the scene,'' Antrim said.

The highway, state route 74, is the major road through the Cleveland National Forest and the Santa Ana Mountains.

''It's a good thing it happened in a remote, mountainous area or else there certainly would have been evacuations,'' Antrim said.