From the same Wikipedia article:
In the 1850s, Eucalyptus trees were introduced to California by Australians during the California Gold Rush. Much of California has a similar climate to parts of Australia. By the early 1900s, thousands of acres of eucalypts were planted with the encouragement of the state government. It was hoped that they would provide a renewable source of timber for construction, furniture making and railroad ties. It was soon found that for the latter purpose eucalyptus was particularly unsuitable, as the ties made from eucalyptus had a tendency to twist while drying, and the dried ties were so tough that it was nearly impossible to hammer rail spikes into them.
"They went on to note that the promise of eucalyptus in California was based on the old virgin forests of Australia. This was a mistake as the young trees being harvested in California could not compare in quality to the centuries-old eucalyptus timber of Australia. It reacted differently to harvest. The older trees didn't split or warp as the infant California crop did. There was a vast difference between the two, and this would doom the California eucalyptus industry."
One way in which the eucalyptus, mainly the blue gum E. globulus, proved valuable in California was in providing windbreaks for highways, orange groves, and other farms in the mostly treeless central part of the state. They are also admired as shade and ornamental trees in many cities and gardens.
Eucalyptus forests in California have been criticised because they compete with native plants and do not support native animals. Fire is also a problem. The 1991 Oakland Hills firestorm which destroyed almost 3,000 homes and killed 25 people was partly fueled by large numbers of eucalypts close to the houses.
In some parts of California, eucalypt forests are being removed and native trees and plants restored. Individuals have also illegally destroyed some trees and are suspected of introducing insect pests from Australia which attack the trees.
Eucalyptus trees do exceptionally well in the Pacific Northwest: Washington, Oregon and parts of British Columbia.