What has four legs, carries nearly three weeks of food at a time, packs as much extra weight as 160 pounds, covers an average distance of 20-plus miles a day and currently is on a summer migration from Canada to Mexico?

That "what is" is really a "who are" - Jim Mayberger and Simon Cordial, who are hiking along the proposed five-state, multi-use Great Western Trail route.Before their June 1 departure from near Priest Lake, Idaho, along the Idaho-British Columbia border, the twosome had known each other for only two days. Now, 63 days, 1,200 miles and a set of boot soles later, the pair are well acquainted - not only with themselves but with the challenges and charms of hiking the West's mountains.

Resuming their southward trek Tuesday, the two recently completed a four-day layover in the Provo area and completed some essential errands - replacing Cordial's broken pack frame, having their hiking boots resoled and allowing Mayberger to rest up from an illness believed to be caused by bad water.

Plus, they had the pleasure of being wined and dined by Provo resident Monroe Gallier, who is credited with conceiving the Great Western Trail concept and who doubles as the Utah volunteer coordinator.

Monday, the two stood at the head of the Ridge Trail - just above the turnoff to Cascade Springs along the Alpine Loop scenic highway - greeting Uinta National Forest officials and politicians such as Lt. Gov. Val Oveson and Utah County commissioners.

The Great Western Trail hike has already taken Mayberger and Cordial along parts of the Idaho-Montana border, through central and eastern Idaho and midway through Utah (alternate northern trails branch into Wyoming and Montana). The two will continue southward, bisecting Utah and Arizona before reaching the U.S.-Mexico border - they hope by the end of October.

The summer-long venture is a lifelong ambition for Mayberger, 26, of Glen Cove, N.Y., who grew up thriving on reading the likes of "Kon Tiki" and the travel journals of Lewis and Clark. Three years ago, he envisioned hiking the United States from Canada to Mexico. Since then, preparation has required thousands of hours, thousands of dollars and thousands of maps.

Last year, he started a similar hike with another companion. However, it was temporarily suspended after 10 days, and his companion was later killed in an unrelated mountain-hiking accident.

Cordial, 26, of Cornwall, England, recalled first meeting Mayberger while spending six months of 1985 hitchhiking across the United States - the two became acquainted as Cordial rested with his pack in a park. The conversation that day led to the two getting together the next year, when Cordial biked from San Francisco to Rhode Island.

In Israel doing volunteer work last fall, Cordial received an unexpected letter from Mayberger, proposing a dual effort in hiking the Great Western Trail.

Since early June, the two have hiked in near isolation - it was 31 days until they met another hiker.

Their meals are an example of fine-tuned preparation, with pre-packaged food left with Mayberger's family to be mailed at a specific date to a specific site. The "site" is a post office box in an accessible city somewhere along the trail route, ranging from Clark Fork, Idaho, to Blue, Ariz.

Since they have to carry food for periods as long as 10 to 20 days, it's no wonder that each pack can weigh as much as 80 pounds - half of that being a full load of food. During some desert stretches, they have had to pack as much as four gallons of water as well.

Although they have registered as official national forest volunteers, Mayberger and Cordial are hiking independently, with no sponsors picking up the estimated $5,000 price tag each for equipment, supplies and travel expenses. However, they plan to provide valuable plotting and logging details for continuing development of the Great Western Trail.