The arrival of the new generation of technology companies and the high salaries they pay to their employees has generated a real estate "boom" in San Francisco that is threatening to change the face of this emblematic city.

The dream that each year attracts thousands of people to this cradle of social movements - including the hippie phenomenon and gay rights - is made concrete in the salaries of more than $100,000 and employee packages including stock options, free food and laundry services as well as free transportation to the headquarters of firms like Facebook, Google and Apple, all of which are located on the peninsula south of San Francisco.

These companies and others based in the city, like Twitter and Zynga, know that many of their employees are people without kids who rent instead of buying and prefer to live in San Francisco itself rather than elsewhere on the peninsula or south of San Francisco Bay, suburbs where families can put down roots.

"Before, about 10 people a week called on a rental ad. Nowadays, more than 100 emails arrive in a day," Eddie Martinez, a real estate professional with 30 years' experience in San Francisco, told Efe.

Rents have risen an average of 12.3 percent in the last year and, at the end of 2013, an ad on Craigslist offered sleeping space on a sofa for $1,075 a month, something that sparked reaction on the social networks.

Buying a house in San Francisco costs about $772,000, while the average yearly income is $72,947, according to census data.

Figures are that 24.4 percent of the city's residents live below the poverty line and some of them even live on the sidewalks outside the buildings where employees receive free pilates classes.

The process whereby the original population of a sector or neighborhood is progressively displaced by another group with higher earning power has created tensions among the residents of the city, who - for instance - have staged demonstrations against the buses that the big tech companies operate to ferry their employees to and from the workplace. EFE