<P> John Muir wrote articles popularizing the area and increasing scientific interest in it . Muir was one of the first to theorize that the major landforms in Yosemite Valley were created by large alpine glaciers, bucking established scientists such as Josiah Whitney, who regarded Muir as an amateur . Muir wrote scientific papers on the area's biology . Landscape architect Frederick Law Olmsted emphasized the importance of conservation of Yosemite Valley . </P> <P> Overgrazing of meadows (especially by sheep), logging of giant sequoia, and other damage caused Muir to become an advocate for further protection . Muir convinced prominent guests of the importance of putting the area under federal protection; one such guest was Robert Underwood Johnson, editor of Century Magazine . Muir and Johnson lobbied Congress for the Act that created Yosemite National Park on October 1, 1890 . The State of California, however, retained control of Yosemite Valley and Mariposa Grove . Muir also helped persuade local officials to virtually eliminate grazing from the Yosemite high country . </P> <P> The newly created national park came under the jurisdiction of the United States Army's Troop I of the 4th Cavalry on May 19, 1891, which set up camp in Wawona with Captain Abram Epperson Wood as acting superintendent . By the late 1890s, sheep grazing was no longer a problem, and the Army made many other improvements . The cavalry could not intervene to ease the worsening condition of Yosemite Valley and Mariposa Grove . The cavalry left another legacy in the park, the ranger hat . From 1899 to 1913, cavalry regiments of the Western Department, including the all Black 9th Cavalry (known as the "Buffalo Soldiers") and the 1st Cavalry, stationed two troops at Yosemite and brought with them the trooper's campaign hat with its distinctive Montana Peak we recognize today as the "ranger hat ." This peak had been formed into the trooper's stetson by veterans of the 1898 Spanish--American War to better shed tropical rain . </P> <P> Muir and his Sierra Club continued to lobby the government and influential people for the creation of a unified Yosemite National Park . In May 1903, President Theodore Roosevelt camped with Muir near Glacier Point for three days . On that trip, Muir convinced Roosevelt to take control of Yosemite Valley and Mariposa Grove away from California and return it to the federal government . In 1906, Roosevelt signed a bill that did precisely that . </P>

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