Franklin Mayor Tom Taylor threw out the first pitch to open the Rock Sports Complex last weekend, and in a couple months someone will take the opening plunge on the mountain bike park being sculpted on the former landfill previously known as Crystal Ridge.

That honor should go to Michael Zimmerman, the health care venture fund president investing $7 million to $9 million to create a world-class recreation destination at the corner of 76th Street and Rawson Avenue. It’s easy to make a "Field of Dreams" connection to Zimmerman’s renovations at the run-down skill hill owned by Milwaukee County. Zimmerman grew up on Rawson Ave., chased his own baseball dreams through high school and still plays in senior hardball leagues. Baseball was his first love.

But at 36, he’s more successful as entrepreneur than first baseman.

Zimmerman joined his father in the health care business in 1996, and started Zimmerman Ventures LLC, a Greenfield-based firm that invests in and manages companies that provide supply, billing, collections and profit management for health care systems. He started one of those firms, Accretive Health in 2002, and sold his stake in 2010.

After that, he bought a vacation property in Steamboat, Colo., and started looking for community-based investment opportunities near his boyhood home. He drove by Crystal Ridge nearly every day, and decided it would be the ideal location for baseball and softball fields.

In September 2012, he signed a deal with Milwaukee County to lease the 142-acre property and started work on The Rock Sports Complex.

His initial idea of two diamonds grew exponentially, much like his businesses. More than a dozen contractors have built 12 ball fields, four for adult baseball leagues, four for youths and four for softball. Six of the fields are replicas of Major League ball parks.

Work crews and heavy equipment, working under the direction of designers from Gravity Logic, have begun to create the mountain bike park, one of four in the country that mix the elements of biking and downhill skiing.

The chairlifts will be rebuilt and retrofitted to carry riders and bikes for the downhill trails – more than a half-dozen - ranging from beginner to intermediate to expert. At the top of the hill, a skills area will offer a pump track, jumps, berms and wall rides.

An expert downhill race track on the slope with 250 feet of elevation has been designed with rock drops, rock gardens and jumps, mimicking the downhill courses on the World Cup circuit.

"It’s going to have a good Colorado feel, a big-mountain feel in a small spot," said Chris Conrad, part of the crew from Gravity Logic, which built the mountain bike parks in Whistler and Colorado.

A narrow trail running uphill along the west edge of the property will connect to the Alpha Trail in Whitnall Park and provide a seven- to nine-mile cross-country loop open to the public for free. The downhill elements will require a fee, and riders will be able to rent the beefed-up bikes necessary for the intense terrain.

A BMX track to replace and improve the layout that existed is also under construction.

The full design can be found on The Rock Sports Complex Facebook page.

Zimmerman’s decision to add the mountain bike park to his "Field of Dreams" was both practical and personal.

Drawing mountain bikers through the summer keeps revenue flowing year-round, not just the few months of winter when skiers buy lift tickets. And Zimmerman fell head-over-handlebars for downhill mountain biking during a test run on the new set-up at Steamboat.

"It was white-knuckle intense," he said. "You cannot take your eyes off what’s in front of you. I have fallen in love with this thing called gravity biking.

"They say that gravity biking is right where snowboarding was before it popped. I hope they’re right."

The transformation at Crystal Ridge, once deemed an eyesore by Taylor and others, has been remarkable.

The pristine fields look out over the wooded western suburbs and the ski area has been reshaped to provide the jumps and berms and wooden features of the downhill mountain bike park. Renovations to the lodge at the top of the hill are ongoing and Zimmerman envisions an outdoor bar area that will hold 100 to 150.

"Look at the fields," said Jim Keegan, acting director of the Milwaukee County Parks Department. "All we had was an ugly eyesore, an old dump that had been capped with grass and weeds.

"This creates a destination area for Milwaukee, a great opportunity for people and kids to play the game of baseball on fields that are major league."

Keegan expects the mountain bike park will become a regional destination.

"They’ll flock to it," he said.

The baseball fields will have a grand opening on June 15, and some of the mountain bike park runs will open then. The full trail system is on schedule to open in early July.