The part that most visitors think of, the Bourbon Street-like atmosphere of Historic Sixth Street, which runs through downtown just beyond Interstate 35, is still a raucous party, with patrons weaving from bar to bar, music blaring through the night and pedicabs darting through crowds. Known locally as “Dirty Sixth,” it draws tens of thousands of college students, music lovers and tourists.

But to the east, past I-35, Mexican restaurants and auto repair shops are mixing with highbrow restaurants, art galleries and hipster bars. Ramshackle cottages are disappearing, and the displacement of working-class families is causing tension in a city that had always prided itself on inclusion.

And to the west is where the city has grown up. It’s where the corporate headquarters of Whole Foods shares the stretch with upscale eateries, such as actress Sandra Bullock’s Bess Bistro and Cafe Josie, and high-end retail stores including Lululemon and Anthropologie. The sidewalks are dwarfed by a surge of new high-rise condos.

Every city is defined by the different personalities of its neighborhoods. For Austin, Sixth Street has become its path and pathology, what it was and what — through a massive boom that has made it one of the fastest-growing cities in the nation — it is becoming.

“You have your young professional and a bit older demographic who are going to West Sixth Street,” said Meredith Sanger of the Austin Downtown Alliance. “Historic Sixth Street attracts the college-aged and tourists who like to come check out the bars, and then you have the east side, which is this interesting up- and-coming area.”

Changes in Austin have driven much of the Sixth Street transformation.

Since 1990, the population has nearly doubled, to about 866,000 in 2014, according to city data. The growth of the tech industry is a big reason, but Austin is also sticking to its “Live Music Capital” reputation. Between 2007 and 2012, employment in the creative sector rose nearly 25 percent, according to the city.

Those trends show all along Sixth Street, said Michael Knox, who creates guidelines for downtown development for the city.

East Sixth

Some consider East Sixth the new frontier, a foodie paradise and bohemian enclave across the interstate from downtown.

“It’s the urban pioneer: Somebody goes over, and they can convert an old warehouse into a bar for minimal money,” Knox said.

But the East Sixth of today came at a cost. Rising property costs and new development are pushing out many longtime residents and established businesses.

Until the 2000s, East Austin was primarily a black and Hispanic neighborhood. The neighborhood’s proximity to downtown and comparatively affordable property led to gentrification.

Cisco’s, an iconic Austin breakfast place, still serves migas in the corner building it’s inhabited since the 1940s. In an old house across the street is La Perla, one of the last-standing Tejano bars and the only place to hear Chente — a Mexican mariachi singer — playing from the jukebox while drinking an armodelo, the bar’s spicy variation on Modelo Especial.

Today, posh eateries, rock music venues and food trucks have moved in where many family-owned Tejano businesses once stood.

On a Saturday night, throngs of 20- and 30-somethings flocked to East Sixth to catch a show at The Liberty or grab drinks at The Brixton. The nightlife here is bustling, not rowdy.

If visitors “are looking to party ... they get bored,” said Tim Lupa, co-owner of The Brixton.

A block from The Brixton, Rio Rita, a coffeehouse and lounge, hosts events such as “Arts and Drafts,” where beer and art projects coalesce, and “Love and a 45,” a night patrons are encouraged to bring in their favorite records.

The whole area is an eclectic mix like that. There’s famed Austin chef Paul Qui’s restaurant, Qui, which serves “multicultural fusion fare” for $65 per plate, just blocks from a food trailer park with trucks dishing out vegan Jambalaya Baton, a gluten-free spicy tofu jambalaya served deep-fried on a stick.

Then there are places like the 6th St. Cool Store, a funky drive-through convenience mart with painted depictions of Bob Marley and Elvis on its storefront that sells craft beers, kombucha, and Mexican Coca-Cola.

“People are just sort of creating; they come up with an idea and find a place for it on East Sixth,” Knox said.

‘Dirty Sixth’

There probably isn’t a University of Texas graduating class since the 1980s unaware of the round-the-clock party scene on Historic Sixth Street.

Thursday, Friday and Saturday nights, the stretch shuts down to traffic, and police are out in force.

Walking the semi-exposed cobbled street on a Friday night means sidestepping half-eaten slices of pizza and navigating through clusters of college-age kids and bachelorette parties debating over which bar to visit next.

Open since 1977, live comedy theater Esther’s Follies has become an institution on Historic Sixth and one of the few places to attract audiences of all ages. With tall windows behind the stage, Follies’ shows have long incorporated in their sketches the antics of the street.

“We’ve had a million people moon us,” said Shannon Sedwick, who owns and performs at the theater.

On Halloween a few years ago, about 10 people dressed as giant bugs came running from the street into the show and stormed the stage, she recalled.

The troupe stood stunned for a moment until suddenly another outsider dressed as a giant can of Raid came running down the aisle, sending the “bugs” scurrying from the stage back out to the street, she said.

There is always that “element of surprise” on Sixth Street, she said.

Despite poking fun at Sixth’s party reputation with skits like “The Wildlife of Sixth St.,” Sedwick and other business owners would like to see history preserved and the nickname “Dirty Sixth” ditched.

Historic Sixth — formerly known as Pecan Street — opened for business more than 170 years ago. It was one of the first integrated parts of Austin, a place where Chinese, black, white and Hispanic business owners mixed on one block. Long-touted landmarks such as the Driskill Hotel and the Ritz Theater neighbored conjunto bars and dry cleaners.

Now, there’s an effort to preserve Pecan Street’s history. A neighborhood association, of which Sedwick is a member, is pinning historic plaques to the centuries-old buildings and lobbying for a gateway arch at the east entrance of the corridor.

Sixth Street has “that sweetness and funkiness,” Sedwick said.

West Sixth

West of Congress Avenue, the architecture on Sixth Street changes from low-rise historic buildings to towering condominiums and modern gleaming construction.

Where Historic Sixth has urban grittiness, West Sixth has modern glossiness. For some, it’s a “yuppified” and less authentic version of Austin.

In 2012, tech firm Cirrus Logic moved into a contemporary building in the 800 block of West Sixth Street. Nearby is GSD&M, formerly called Idea City, an Austin advertising agency that helped elevate brands such as Southwest Airlines and Chipotle. Facebook opened its corporate office on West Sixth Street in 2010.

“There used to be more families. Now it’s a lot of young professional types, singles and groups meeting to go out for drinks,” said Mike Hutchinson, owner since 1982 of the well-known West Sixth burger joint Hut’s Hamburgers.

Local haunts are tucked within the corporate milieu. Across from the Whole Foods headquarters at Sixth and Lamar Boulevard is Waterloo Records, a favorite local independent music store since 1981.

Not far away, music heads dance at The Belmont, a venue where performances range in one night from the North African group Tinariwen to Home Alone star Macaulay Culkin’s parody band the Pizza Underground.

The end is “microcosmic” of greater changes in Austin — the booming tech industry, corporate relocations to downtown and an in-rush of newcomers — said John Kunz, owner of Waterloo Records.

“There’s an awful lot of people I know who are not happy about all the condos and apartments that have gone up downtown, but I’d rather see greater height and density” than sprawl taking over the Hill Country, he said.

“Back 30 and 40 years ago, I was one of the folks trying to discourage the growth and so forth that happens here,” he said. “We finally realized we weren’t going to be able to stop folks from coming here. It’s been more of a matter of how you try to manage it.”