Jim Thomsen grew up in California and became interested in mountaineering and outdoor recreation after spending many summers in Mammoth Lakes, California with his father and his brother, Greg. In 1965, both Jim and Greg began backpacking across California's Sierra and eventually picked up climbing in 1967. While Jim was working at Kelty Pack around this time, his wife Laurie suggested starting an outdoor mountaineering recreation program specifically for youth. Jim, Greg, and Laurie chose to call the program Wilderness Experience and began teaching cross-country skiing, backpacking, and climbing.

In 1971, Jim and Greg started making small accessories for their guides to use on Wilderness Experience tours and also sold them at the Mountain Store in Tarzana, California, which they both managed. The brothers met Class 5 owner Justus Bauschinger in 1972 who encouraged and helped Jim and Greg to create a more complete line of outdoor recreation gear. They began making gaiters but became known for packs when their line was taken on by Don Lauria at his store Westridge Mountaineering in Santa Monica, California. They also began making sleeping bags and tents but kept their concentration on packs, eventually adding the tagline "We only make backpacks and that's why we're the best" to their advertisements and pamphlets between 1974 and 1975.

Wilderness Experience was one of the early sewing companies to have computerized systems due to Jim's fascination with computers. All of their merchandise was created in-house including small accessories. By 1980 the company was a major outdoor industry manufacturer with factories in Chatsworth, North Hollywood, and San Francisco, California where they employed a few hundred workers. Jim left Wilderness Experience in 1983 and taught classes at California State University Northridge based on small business and outdoor recreation.