A mock city roughly the size of downtown San Diego has risen in a remote Southern California desert to train military forces to fight in urban environments. The $170 million urban training center was unveiled [on January 25] at the Twentynine Palms military base, 170 miles northeast of San Diego. The 1,560-building facility will allow troops to practice and refine skills that can be used around the world, the Marine Corps said. The military has been opening a slew of mock Afghan villages at bases across the country to prepare troops for battle before they are deployed. The new training center is one of the largest and most elaborate. Seven separate mock city districts spread across 274 acres of desert. The facility has almost 1,900 feet of underground tunnels, a manmade riverbed and dozens of courtyards and compounds. More than 15,000 Marines and sailors can train simultaneously in the massive simulator to experience the difficulties they will face during deployments. The new center expanded a similar training program called Mojave Viper that launched in 2005 to prepare troops for the Iraq war. In November, the Marine Corps unveiled a $30 million expansion of its mock Afghan village at Camp Pendleton that nearly quadrupled its size. Similar immersion training facilities are slated to open this year at Marine Corps bases in North Carolina, Hawaii and Okinawa.