One of the important themes in Trespassing Across America are, as the title suggests, trespassing—the violation of legal boundaries. In walking the 1,700 mile route of the Keystone XL Pipeline, Ilgunas set foot without the owner’s permission on a considerable amount of private land, which constitutes trespassing. Before beginning the trip, the author conducted research to determine the route of the proposed Keystone Pipeline. As it wends its way through Canada into the United States down to its Southern border, the route crosses the properties of a wide assortment of owners. Ilgunas realized just by walking across these diverse lands, he would trespass on private property as a daily practice. While he sometimes passed unnoticed, his more frequent interactions with various landlords greatly expanded his understanding of American attitudes toward land as property and productive resource, and diverse notions of stewardship.

Two other main themes that Ken Ilgunas addresses are ecology and environmentalism. One of his goals was to understand the impact that the pipeline would have on the North American plains environment. Ilgunas’ motivations for walking the route included his interest in ecology, with the desire to see for himself the environments that would be affected. He was concerned that the drilling and tunneling would disrupt the natural and cultural landscapes through which it would pass. He aims to situate the rationale for the pipeline’s construction and its desired output in a larger social and economic picture. His experiment brought him a greater appreciation of the fragility of not just land, but water, and the irreversible nature of the changes that would be wrought.

Two other main themes that Ken Ilgunas addresses are self-reliance. In doing the journey alone, Ilgunas needed discipline and self-confidence, characteristics associated with American individualism. Like many naturalists before him, Ilgunas wanted to walk this journey alone. He saw his commitment to self-reliance as meaning that he was striving individually to attain certain goals and was not dependent on others to accomplish them. He learned, however, that his success did depend on human kindness. His deeply felt personal connection with the environment had spiritual elements, and he felt it was important to confront nature on his own terms. In this way, the physical journey matched an interior journey toward self-knowledge. While the devotion to learning through nature was an element of earlier American literature, it was most well developed by the mid-19th-century New England Transcendentalists, especially Ralph Waldo Emerson and his essay on self-reliance, and related thinkers such as Henry David Thoreau.