"I want to ensure that these majestic cathedral groves, which John Muir called 'nature's masterpiece,' are protected for future generations to study and enjoy," Clinton wrote.

Naturalist Muir's writings helped create the U.S. conservation and environmental movements. With lifespans of over 3,000 years, the evergreen giant sequoias are one of the largest trees on the planet, reaching diameters of more than 30 feet (nine metres) and heights of 325 feet (100 metres). They grow in just 75 groves on the western slopes of the Sierra Nevada mountain range.

The National Resources Defence Council, an environmental group, has been pressing the government to create a new Giant Sequoia National Monument to provide permanent protection for the sequoia forests.

On Jan. 11, Clinton invoked the 1906 Antiquities Act to declare a million acres of federally owned land on the north rim of the Grand Canyon as a national monument. The designation put the land off limits to new mining and other forms of development.

Environmentalists applauded the step, while local officials complained Clinton should consult with them before acting. The new million-acre (405,000 hectare) preserve, encompassing a tributary of the Colorado River, was almost as big as the Grand Canyon National Park.

Carved by the Colorado River, the Grand Canyon is a chasm 277 miles (445 km) long, up to 18 miles (28 km) across and a mile (1.6 km) deep.

In the letter to Glickman, Clinton asked for a recommendation within 60 days whether prudent stewardship warranted permanent protection of the sequoia groves. He directed officials to consult with tribal, state and local officials as well as forestry experts.