Thumb Mountain is a 1978 feet (602.9 m) steep-sided monadnock

Monadnock

A monadnock or inselberg is an isolated rock hill, knob, ridge, or small mountain that rises abruptly from a gently sloping or virtually level surrounding plain...

 located in Hancock, New Hampshire

Hancock, New Hampshire

Hancock is a town in Hillsborough County, New Hampshire, United States. The population was 1,654 at the 2010 census. Hancock is home to the Welch Family Farm Forest....

 approximately 13 mi (20.9 km) east of the city of Keene

Keene, New Hampshire

Keene is a city in Cheshire County, New Hampshire, United States. The population was 23,409 at the 2010 census. It is the county seat of Cheshire County.Keene is home to Keene State College and Antioch University New England, and hosts the annual Pumpkin Fest...

 and 8 mi (12.9 km) north of Mount Monadnock

Mount Monadnock

Mount Monadnock, or Grand Monadnock, is the most prominent New England mountain peak south of the White Mountains and east of the Massachusetts Berkshires, and is the highest point in Cheshire County, New Hampshire...

. The mountain shares a common base with Skatutakee Mountain

Skatutakee Mountain

Skatutakee Mountain is a monadnock located in Hancock, New Hampshire approximately east of the city of Keene and north of Mount Monadnock. The mountain shares a common base with Thumb Mountain, , to the west...

, 1998 feet (609 m), 3000 feet (914.4 m) to the east. Much of the mountain is wooded but open ledges near the summit provide views of the surrounding countryside; vistas include the north face of Mount Monadnock.

The west side of the mountain drains into Nubanusit Lake

Nubanusit Lake

Nubanusit Lake is a lake located on the border between Cheshire and Hillsborough counties in southwestern New Hampshire, United States, in the towns of Nelson and Hancock. The outlet of the lake is Nubanusit Brook, a tributary of the Contoocook River in the Merrimack River drainage basin....

, Brickyard Brook, Harrisville Pond

Harrisville Pond

Harrisville Pond is a water body located in Cheshire County in southwestern New Hampshire, in the town of Harrisville. It is one of many lakes and ponds along Nubanusit Brook. Water from Nubanusit Lake flows via the Great Meadows into the pond on the north side and out of the pond at two dams on...

, Skatutakee Lake

Skatutakee Lake

Skatutakee Lake is a water body located in Cheshire County in southwestern New Hampshire, in the town of Harrisville. Water from Skatutakee Lake flows via Nubanusit Brook to the Contoocook River in Peterborough, New Hampshire and ultimately to the Merrimack River....

, thence into Nubanusit Brook

Nubanusit Brook

Nubanusit Brook is a stream located in southern New Hampshire in the United States. It is a tributary of the Contoocook River, part of the Merrimack River watershed.Nubanusit Brook begins at the outlet of Nubanusit Lake in Nelson, New Hampshire...

, the Contoocook River

Contoocook River

The Contoocook River is a river in New Hampshire. It flows from Pool Pond and Contoocook Lake on the Jaffrey/Rindge border to Penacook , where it empties into the Merrimack River. It is one of only a few rivers in New Hampshire that flow in a predominantly northward direction...

, the Merrimack River

Merrimack River

The Merrimack River is a river in the northeastern United States. It rises at the confluence of the Pemigewasset and Winnipesaukee rivers in Franklin, New Hampshire, flows southward into Massachusetts, and then flows northeast until it empties into the Atlantic Ocean at Newburyport...

, and the Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

. The east side drains into Jaquith Brook, thence into Nubanusit Brook. The north side drains into Ferguson Brook, thence the Contoocook River.

The mountain is part of a 12500 acres (50.6 km²) "supersanctuary" composed of a number of conservation properties and easements facilitated by the Harris Center for Outdoor Education, other non-profit entities, and the state of New Hampshire

New Hampshire

New Hampshire is a state in the New England region of the northeastern United States of America. The state was named after the southern English county of Hampshire. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Atlantic Ocean to the east, and the Canadian...

. The Harris Center maintains several hiking trails on the mountain and an environmental educational center at the mountain's north foot.