<P> In 1870, non-natives began grazing cattle on the tall grasses that grew in the park . In 1888, a gang of cattle rustlers moved into the region near the Oasis of Mara . Led by brothers James . B. and William S. McHaney, they hid stolen cattle in a box canyon at Cow Camp . Throughout the region, ranchers dug wells and built rainwater catchments called "tanks", such as White Tank and Barker Dam . In 1900, C.O. Barker, a miner and cattleman, built the original Barker Dam, later improved by William "Bill" Keys, a rancher . Grazing continued in the park through 1945 . Barker Dam was added to the National Register of Historic Places (NRHP) in 1975 . </P> <P> Between the 1860s and the 1940s, miners worked about 300 pit mines, mostly small, in what later became the park . The most successful, the Lost Horse Mine, produced gold and silver worth about $5 million in today's currency . Johnny Lang and others, the original owners of the Lost Horse Mine, installed a two - stamp mill to process ore at the site, and the next owner, J.D. Ryan, replaced it with a 10 - stamp steam - powered mill . Ryan pumped water from his ranch to the mill and cut timber from the nearby hills to heat water to make steam . Most of the structures associated with the mine fell apart, and for safety reasons the National Park Service plugged the mine, which had collapsed . The Desert Queen Mine on Keys' Desert Queen Ranch was another productive gold mine . In the early 1930s, Keys bought a gasoline - powered two - stamp mill, the Wall Street Mill, and moved it to his ranch to process ore . The ranch and mill were added to the NRHP in 1975 and the mine in 1976 . Some of the mines in the park yielded copper, zinc, and iron . </P> <P> On August 10, 1936, after Minerva Hoyt and others persuaded the state and federal governments to protect the area, President Franklin D. Roosevelt used the power of the 1906 Antiquities Act to establish Joshua Tree National Monument . It protected about 825,000 acres (334,000 ha). In 1950, the size of the park was reduced by about 290,000 acres to open the land to more mining . The park was elevated to a National Park on October 31, 1994, by the Desert Protection Act, which also added 234,000 acres to the park . </P> <P> The higher and cooler Mojave Desert is the special habitat of Yucca brevifolia, the Joshua tree for which the park is named . It occurs in patterns from dense forests to distantly spaced specimens . In addition to Joshua tree forests, the western part of the park includes some of the most interesting geologic displays found in California's deserts . The dominant geologic features of this landscape are hills of bare rock, usually broken up into loose boulders . These hills are popular among rock climbing and scrambling enthusiasts . The flatland between these hills is sparsely forested with Joshua trees . Together with the boulder piles and Skull Rock, the trees make the landscape otherworldly . Temperatures are most comfortable in the spring and fall, with an average high / low of 85 and 50 ° F (29 and 10 ° C) respectively . Winter brings cooler days, around 60 ° F (16 ° C), and freezing nights . It occasionally snows at higher elevations . Summers are hot, over 100 ° F (38 ° C) during the day and not cooling much below 75 ° F (24 ° C) until the early hours of the morning . </P>

When did joshua tree became a national park