A dusty half-mile trail separated the houses where cousins Mark and Tom Udall grew up in Tucson, Ariz. As boys, they traversed the distance by bike or by pony.

Now, the men have offices two floors apart in the Hart Senate Office Building, and the Democratic Senators from Colorado and New Mexico, respectively, can reach each other easily on foot.

Three years into their first terms, each is finding his own path in the Senate, where the terrain can be as rocky as the Arizona desert. On the way, they have set themselves apart — from their Democratic caucus, from the long shadows cast by their famous fathers and even from one another.

“They have both already developed a reputation for reaching out across the aisle,” says Sen. John McCain (R-Ariz.), who considered Mark’s late father, Rep. Morris “Mo” Udall (D-Ariz.), a mentor. “They are good fits for their states, which are pretty independent.”

Tom, 62, made waves this month in the notoriously slow-to-change chamber when he championed the overhaul of one of the institution’s signature mechanisms, the filibuster. Although his colleagues voted down his plan to weaken the filibuster’s bill-killing powers, it sparked debate and put him at odds with Democratic leaders.

Mark, 60, lately has also displayed an independent streak. He was behind the bipartisan seating arrangements during the State of the Union address. And he was the first Democrat last week to support a GOP-backed balanced budget amendment.

Those recent moves have raised the profiles of the Udall cousins, but their newly prominent, contrarian roles are an outgrowth of their quirky Western personas.

“Over here, you have two great Americans,” Mark says on a recent afternoon, motioning to a framed photo displayed in Tom’s Senate office. It is a black-and-white snapshot of his father and Tom’s father, Stew Udall (D-Ariz.), the late former Congressman and secretary of the Interior. “And here,” he says, picking up another picture, “you’ve got two bums.”

This frame reveals Mark and Tom on a long-ago mountain-climbing trip. Neither is certain of the year it was taken, but their beards and sideburns put it sometime in the 1970s. Both men smile at the memory. But neither needs a photo to remind them of their shared history or their family legacy.

To ask about their own roles in the Senate is to hear about Mo and Stew and the Udall tradition. Both trace their interest in politics to their fathers and credit them with their focus on environmental issues.

“We’re not going to ever fill those shoes, but we can follow the direction their boot-steps lead,” Mark says. He is the wilder of the two, more prone to wise-cracking. Tom’s humor is more understated. He takes notes while he listens, and his hair is neatly combed in place, where Mark’s flops onto his forehead.

Even though they are pursuing distinct agendas, colleagues tend to view the Udalls as a team. This is only natural, since the cousins’ careers have taken them on remarkably similar paths: They both served in the House from 1999 to 2008, when they moved across the Capitol Dome to the Senate.

In the House, they were often seen sitting together on the floor during votes. In the Senate, they requested adjacent desks.

“I certainly see them as chips off their fathers’ blocks,” says former Sen. Gordon Smith (R-Ore.), who is a second cousin of both men. Like many Mormon families, the Udall family tree is complicated by polygamy; Smith’s grandfather was the son of one of patriarch David King Udall’s two wives, while Tom and Mark’s grandfather was the son of the other wife.

Bipartisanship, he says, is a lesser-known part of the Udall legacy.

Smith, who is now president of the National Association of Broadcasters, was himself a frequent aisle-crosser in his Senate days and knows that being a moderate isn’t always rewarded.

“It’s where the action is, but it’s a dangerous place to be,” he says of centrist territory. “The political process is often not kind to peacemakers and deal-makers.”

Tom and Mark, though, are armed against the potential ravages with a potent weapon: likability. Colleagues almost unanimously use a word that’s rare in politics to describe them — nice.

“They are just pleasant and delightful people,” says Sen. Mike Lee (R-Utah), who is, surprisingly, another distant Udall cousin. His tea party backing and staunch conservatism often put him at political odds with his Democratic kin, but they get along personally.

“They’ve inherited this calm inner decency and genuine friendliness,” McCain says. “They are personable.”

Others note that the Udalls’ familiarity with the Senate and relationships they developed in the House have served them well. “They came to the Senate extremely knowledgeable about how things work around here,” Sen. Jeff Bingaman (D-N.M.) says. “It’s allowed them to be quite effective.”

So far, their achievements remain works in progress. Tom is still pressing for filibuster reform, although he has acknowledged the effort is dead for now. He realizes changing Senate rules isn’t the sexiest cause.

“In the House, people would say not to talk about procedure, but I think people understand the filibuster,” he says. “They get it.”

Mark, meanwhile, is anxious to build on the success of the bipartisan seating during the president’s speech. He is an unlikely deficit hawk, too, something he didn’t think would become one of his primary concerns.

“If you asked me a few years ago, I would have said that I’d be working on green energy — but these are the challenges in front of us,” he said.

In the House, their biggest joint effort was on legislation boosting the use of renewable electricity. While the House passed their measure several times, it never cleared the Senate, and they now are hoping to push similar clean-energy legislation in the chamber.

The cousins face some daunting non-legislative challenges, too. Mark, who worked for the Outward Bound program for 20 years, has scaled all 54 “14-ers” — mountains with peaks above 14,000 feet — in his home state and now is working on the 13-ers.

“We’ve got to plan another trip,” says Tom, an avid climber himself.

Mark has even bigger plans than heading to Colorado.

“You know what?” he says with a gleam in his eye. “We should try Antarctica.”