Later he held two significant public appointed posts: chief of forestry in the Bureau of Indian Affairs, from 1933 to 1937, and head of recreation management in the Forest Service, from 1937 to 1939, both during the administration of President Franklin D. Roosevelt.

Defining wilderness as a social as well as an environmental ideal, Marshall promoted organization of a national group dedicated to the preservation of primeval land.

The Act was passed by Congress in 1964 and legally defined wilderness areas of the United States and protected some nine million acres (36,000 km2) of federal land from development, road building and motorized transportation.

[6] An amateur naturalist and active conservationist, Louis Marshall was instrumental in securing "forever wild" protection for the Adirondack and Catskill Forest Preserves in New York State.

[10] His younger brother George (1904–2000) later described the family's visits to Knollwood, their summer camp on Lower Saranac Lake in the Adirondack State Park, as a time when they "entered a world of freedom and informality, of living plants and spaces, of fresh greens and exhilarating blues, of giant, slender pines and delicate pink twinflowers, of deer and mosquitoes, of fishing and guide boats and tramps through the woods".

He discovered his passion for exploring, charting, and a love of climbing mountains, in part through the writings of Verplanck Colvin, who during the post-Civil War decade surveyed the woods of northern New York.

In 1915, Marshall climbed his first Adirondack peak, the 3,352-foot (1,022 m) Ampersand Mountain, alongside his brother George and family friend Herb Clark, a Saranac Lake guide.

Marshall had decided in his teens that he wanted to be a forester, writing then about his love of "the woods and solitude;" he wrote that he "should hate to spend the greater part of my lifetime in a stuffy office or in a crowded city".

In 1922, he became one of the charter members of the Adirondack Mountain Club (ADK), an organization devoted to the building and maintenance of trails and the teaching of hiking in the park.

"[22] In the early morning when the first faint light Cuts the murky blackness of the cool calm night, While the gloomy forest, dismal, dark, and wild, Seems to slowly soften and become more mild,

When the mists hang heavy, where the streams flow by And reflects the rose-tints in the eastern sky, When the brook trout leaps and the deer drinks slow, While the distant mountains blend in one soft glow,

[12] The senior yearbook described him as "the Champion Pond Hound of all time, a lad with a mania for statistics and shinnying mountain peaks, the boy who will go five miles [8 km] around to find something to wade thru.

[30] Spending time with loggers and fire fighters, and seeing the conditions under which they worked, Marshall learned vital lessons about labor issues and natural resource use.

[33] After leaving the Forest Service in 1928, Marshall worked to complete his studies for a PhD in plant physiology at Johns Hopkins University in Baltimore, Maryland.

The following year he made his first trip to Alaska, visiting the upper Koyukuk River and the central Brooks Range, and preparing for an extended stay for study.

[35] He placed the desk so that he could sit by the cabin's single window and admire the view of the Koyukuk River and the range of steep, snow-covered mountains in the background.

[51] In particular, he was concerned that few articles of this time addressed the issue of deforestation, and he wrote a letter to the president of the American Forestry Association, George D. Pratt, on the matter.

Marshall besieged government personnel with letters, telephone calls, and personal visits in the cause of wilderness, rapidly gaining recognition in Washington as a champion of preservation.

[62] One of his last initiatives as chief forester of the BIA was to recommend designation of 4,800,000 acres (19,425 km2) of Indian reservation lands for federal management as either "roadless" or "wild" areas.

The administrative order, which created 16 wilderness areas, received approval shortly after Marshall left the BIA to join the Forest Service again.

The smell of pine needles and flowers and herbs and freshly turned dirt and all the other delicate odors of the forest are drowned in the stench of gasoline.

[63]In 1934, Marshall visited Knoxville, Tennessee and met with Benton MacKaye, a regional planner who gained support to designate and lay out the Appalachian Trail.

[64] Bernard Frank, a fellow forester, joined them later in the year; the men mailed an "Invitation to Help Organize a Group to Preserve the American Wilderness" to like-minded individuals.

The invitation expressed their desire "to integrate the growing sentiment which we believe exists in this country for holding wild areas sound-proof as well as sight-proof from our increasingly mechanized life," and their conviction that such wildernesses were "a serious human need rather than a luxury and plaything".

"One could comfortably argue," Watkins wrote in 1985 on the occasion of the society's 50th anniversary, "that Robert Marshall was personally responsible for the preservation of more wilderness than any individual in history".

[69] Marshall was too busy traveling to respond to the allegations: after leaving Alaska he spent time in Washington state, Montana, Oregon, Nevada, Utah, Arizona, New Mexico and California.

[71] While Marshall was in Washington State that September, two regulations (U-1 and U2) developed by his Forest Service committee were signed by Secretary of Agriculture Henry A. Wallace; these "U-Regulations"[72] protected wilderness and wild areas from road building, logging, hotels, and similarly destructive activities.

Trustees of the latter trust included Robert Sterling Yard, Bob Marshall's brother George, Irving Clark, Olaus Murie and Bill Zimmerman, early leaders of The Wilderness Society.

[3] Marshall's posthumously published book Alaska Wilderness, Exploring the Central Brooks Range (1956), edited by his brother George, became a seminal work.

According to the publisher, the book includes "numerous accounts of his hikes in the High Peaks and the vast wild region south of Cranberry Lake, spirited defenses of the state's forever-wild Forest Preserve, a charming portrait of Herb Clark, and excerpts from an unpublished novel set partly in the Adirondacks".