On one side of the freeway that slices through this city's southern skyline are the lofty office buildings where high-priced executives come to work in chauffeured Mercedes cars and make this city the most powerful commercial and financial capital on the continent.

On the other side rise huge, pale yellow mounds of earth that are the city's distinctive trademark. These hills contain the churned-up, crushed insides of the gold mines that gave birth to Johannesburg and make it, almost 100 years later, the hub of a mining industry providing 72 percent of the noncommunist world's gold.

Today these gold dumps, as they are popularly known, are no longer just mementos of Johannesburg's heritage. They have become some of the most valuable property in town. The high price of gold has made it worthwhile for the dumps to be "reprocessed" to remove the gold that older and less efficient extraction methods left behind.

During the next decade many of the dumps will disappear as they are shipped truckload by truckload, to retreatment plants and then redeposited elsewhere. Their removal will provide space for more offices and factories, a prospect that has upset traditionalists who decry the mining companies' fiddling with "our Tower of London," as one resident called the dumps.

Rand Mine Properties, which owns several of the dumps closest to town, has decided to build a $52 million plant that will extract 30 tons of gold from 60 millions tons of ore and sand in their dumps during the next 12 years. The retreated material will be redeposited on top of other dumps, making more than 200 acres available for property development, according to managing director Paul Forbes.

"Remining" the dumps, however, is only one of the spinoffs of the high gold price in this city that blacks know as Egoli or "city of gold," a city whose folklore, aura and prosperity are entwined with the yellow metal that investors throughout the world are grabbing as a hedge against inflation.

A metal that by itself, in the first six months of this year, gave mining companies pretax earnings of $4.8 billion, more than they got from gold sales in all of 1979; that in the same period gave the state $2.6 billion in taxes, and that has been mainly responsible for an economic boom giving the country an 8 percent growth rate and Johannesburg a runaway real estate market.

Gold used to be sold at a set price of about $40 an ounce, an artificial rate determined by the United States. But in 1968 a two-tiered system was introduced keeping the official price for central bank dealings but letting market forces set the price for all other purchases. In 1971, an International Monetary Fund agreement eliminated the official price.

Since then the gold price has risen by leaps and bounds, the most spectacular rise occurring between January 1979 and January 1980 when gold moved from $200 to $850 an ounce. After that peak, the price has settled back to an average of $600 during the last few months.

In the modernistic Johannesburg stock exchange, glass elevators glide silently up and down the walls of its cavernous foyer like crystal ladybugs. Next to the desk of Richard Lomberg, a young, straight-backed stockbroker a television screen scans the boards on the floor of the exchange where 54 gold mines are listed.

"There are mines we paid absolutely no attention to in the 'bad old days' of gold [when its price was officially set]. Many of them were listed on the exchange merely as a matter of historical coincidence and nothing else," Lomberg said.

"Now there's interest from London on a large scale in the sorts of 'rats and mice' shares they would just not have been interested in before," he said. "We're getting to the stage that if you have a hole in the ground that used to have gold in it, the price of the hole is going up."

The higher gold price is also sending miners deeper. At 2.3 miles, Western Deep Level, which belongs to the huge mining conglomerate Anglo-American, is already the deepest gold mine in the world. In July, Anglo announced it will sink another mine shaft that by 1992 will go 300 feet deeper than its deepest shaft and cost $975 million.

New mines unthinkable when gold was pegged to a fixed price, are swinging into operation.

Max Borkum, a balding stockbroker who has been urging gold shares on his clients for years, now has done one better. With several associates, he bought the oldest working mine on the Witwatersrand, the plateau where the reefs, the gold-speckled layers of quartz, were discovered in 1886.

To call his purchase, Simmer and Jack, a "working" mine was stretching it a bit. It was one of the richest mines in Johannesburg's heyday in the early 1900s, but an official gold price and rising costs meant Simmer and Jack had to close in 1964. Its hospital and warehouses were rented out to bring in a little money.

But two months ago, the new owners arranged a deal with Anglo-American to open a second shaft and expand production.

"It's quite romantic really," said Borkum using an adjective only a stockbroker would employ to describe how Simmer and Jack's share prices stood at 70 cents when it was bought in May 1979 and now are worth $6.

Although mining is the biggest of big businesses in South Africa, with six mining "houses" controlling the bulk of it, a few individuals manage to cash in on the bonanza as modern-day "prospectors." One of them is a Portuguese immigrant, Jose Manuel Rodrigues Berardo.

"I used to see those big 'mountains' and I always thought the gold price would go up," he said. "I began to apply for the rights on some dumps in 1973. A lot of people wanted to get rid of them. I bought some very cheap. 'I will try to move this mountain,' I told them. At the time they thought it was impossible. They thought I was a bit cuckoo. But now everybody is fighting for what I've got."

Out on the "East Rand," as Johannesburg residents call the farming and mining land around the tiny town of Nigel, Berardo showed off his company's latest purchase -- a stubby-grassed, flat-topped, 600-acre hill that is estimated to hold 32,000 pounds of gold. At today's price, it is theoretically worth $307 million.

"I think the day will come when we'll see, like in the old days, currency of gold. For how long can the governments go on printing paper money that has no value? I don't think it will work out in the long run."

Meanwhile, Berardo has another idea on how to capitalize on the high gold price and the gold fever it has produced.

"I think I'll put sand from the dump, after I've treated it into little bags that say, 'This contains .0002 percent of gold' and sell them in America.

"If Americans will buy cans of fresh air and I've seen them do it, why won't they buy bags of gold? I think they will."