Cat Whitehill Long the heir apparent to legendary center back Joy Fawcett, and on pace to eventually pass Fawcett as the most-capped defender in history, the 25-year-old Whitehill is the cornerstone of the American back line. Like most great center backs, she is at her best in anticipating and defusing trouble before it necessitates spectacular individual plays, but she also has the size and speed to react and dispossess as the last line of defense. In addition to her role in the center of the defense, Whitehill is a valuable offensive weapon on the set pieces that produce so many goals and help set the United States apart from the rest of the world. With a booming leg, Whitehill takes most of the long free kicks and has a knack for putting the ball on goal, and near Wambach's head, from distances at which few other teams would even think of trying to go for goal. And while she undeniably caught a few good breaks along the way, her five goals in 16 games last year speak to what she can contribute with her feet and her head on the other end of the field. Christie Rampone Arguably the most underrated player on the U.S. roster, Rampone quietly leaves Ryan with little to worry about from her spot on the back line, whether it is outside, inside or a little bit of both. A veteran of both the 1999 World Cup, where she played in one match, and the 2003 World Cup, where she started four games (notably not including the semifinal loss against Germany for which she was on the bench), Rampone is ninth in all-time appearances for the United States and could move into eighth during the World Cup. Like Lilly, Rampone has defied the logical aging process, maintaining the elite speed that allows her to play outside and push forward on a regular basis. Through the end of July, she had played every minute of 10 starts this season, a stretch of minutes that included a stint as captain during a game at the Algarve Cup. Kate Markgraf One of only two veterans of the 1999 World Cup starting lineup, along with Lilly, likely to start again in China (with Brianna Scurry set to be the No. 2 keeper), Markgraf is an especially key player now that Heather Mitts' injury has depleted the back line and left little in the way of flexibility for Ryan. She admitted to rushing her return from giving birth last year in time to play extended minutes at the Four Nations Cup in January, but she played a full 90 minutes in four consecutive games against Brazil, China, Norway and Japan in June and July, numbers that suggest a player known for her fitness and endurance is rounding back into top form. Playing mostly on the inside of Ryan's four-back alignment now after many years as an outside back, Markgraf teams with Cat Whitehill to provide a generally young team with nearly 400 games of experience and poise at the heart of the defense. Comfortable in a leadership role, Markgraf is also a vocal and willing on-field mentor for younger players like Lopez. Stephanie Lopez The only active college player on the roster, Lopez will trade in a good portion of her senior season at the University of Portland for a starting spot at outside back in the World Cup. Lopez earned her first cap little more than two years ago at the Algarve Cup but she had already thrust herself into contention for a key role in China before projected starter Heather Mitts went down with a torn ACL this spring, ensuring Lopez would be the frontrunner to start. Lopez has as much offensive upside as any outside back on the roster -- she was tied this year with Lilly and Tarpley for the team lead with three assists through the end of July. Ryan has experimented with playing her in the midfield in a 3-4-3 formation, but she looked the most comfortable coming forward from outside back. At this point, she may not be as consistent a one-on-one defender as Mitts, but she is a true two-way player and is perfectly willing to stick her nose in and put in the work on the defensive end. Tina Ellertson Formerly known as Tina Frimpong, Ellertson is the extent of the team's experience off the bench for the back line (assuming Chalupny remains in midfield). She started 10 games last year, mostly during the first half of the year, before shifting to a reserve role as Stephanie Lopez established herself at outside back and Kate Markgraf returned in the middle of the back line after giving birth. The team allowed just four goals in her 10 starts last year, and two of those came after she came off in the second half of a game against Sweden. In addition to an inspirational personal story worthy of its own spotlight, having starred at the University of Washington after nearly giving up her soccer career due to a pregnancy before her freshman year of college, she may well merit attention on the field in China. A forward in college, Ellertson still has tremendous offensive instincts and may be the fastest player on the roster. She has shown versatility at her new position, playing both outside and in the middle for the United States. Marian Dalmy The biggest surprise on the final roster -- she is the only player going to China who didn't even merit inclusion in the team's 2007 yearbook, and she didn't earn her first cap until coming on as a reserve against Mexico in April -- Dalmy has emerged as a potential future starting outside back for the national team after an injury-marred career at Santa Clara. Dalmy certainly had her moments with the Broncos, earning West Coast Conference Player of the Year honors as a senior in 2006, but a torn ACL suffered in the team's final game of the 2005 season limited her international availability. An offensive-minded outside back in college, although she also played some at midfield and forward, she has tremendous size and has adjusted well to Ryan's demanding defensive schemes. Graham Hays is a regular contributor to ESPN.com's soccer coverage. E-mail him at Graham.Hays@espn3.com.