It is a large deciduous coniferous tree reaching 30 to 60 metres (98 to 197 feet) tall, with a trunk up to 1.5 m (4 ft 11 in) diameter.
The largest known western larch is 47 m (153 ft) tall and 6.7 m (22 ft) in circumference with a 10 m (34 ft) crown, located at Seeley Lake, Montana.
The crown is narrow conic; the main branches are level to upswept, with the side branches often drooping.
The shoots are dimorphic, with growth divided into long shoots (typically 10 to 50 cm (4 to 20 in) long) and bearing several buds, and short shoots only 1 to 2 mm (¹⁄₃₂ to ³⁄₃₂ in) long with only a single bud.
The leaves are needle-like, light green, 2 to 5 cm (³⁄₄ to 2 in) long, and very slender; they turn bright yellow in the fall, leaving the pale orange-brown shoots bare until the next spring.

The seed cones are ovoid-cylindric, 2 to 5 cm (³⁄₄ to 2 in) long, with 40 to 80 seed scales; each scale bearing an exserted 4 to 8 mm (³⁄₁₆ to ⁵⁄₁₆ in) bract.
The cones are reddish purple when immature, turning brown and the scales opening flat or reflexed to release the seeds when mature, four to six months after pollination.
The old cones commonly remain on the tree for many years, turning dull gray-black.

It grows at elevations between 500 and 2,400 m (1,600 and 7,900 ft), and is very cold tolerant, able to survive winter temperatures down to about −50 °C (−58 °F).
It only grows on well-drained soils, unable to thrive on waterlogged ground.

The seeds are an important food for some birds, notably pine siskin, redpoll, and Two-barred crossbill.

In autumn, the foliage frequently turns yellow before it falls off.
It is a large deciduous coniferous tree reaching 30 to 60 metres (98 to 197 feet) tall, with a trunk up to 1.5 m (4 ft 11 in) diameter. The largest known western larch is 47 m (153 ft) tall and 6.7 m (22 ft) in circumference with a 10 m (34 ft) crown, located at Seeley Lake, Montana. The crown is narrow conic; the main branches are level to upswept, with the side branches often drooping. The shoots are dimorphic, with growth divided into long shoots (typically 10 to 50 cm (4 to 20 in) long) and bearing several buds, and short shoots only 1 to 2 mm (¹⁄₃₂ to ³⁄₃₂ in) long with only a single bud. The leaves are needle-like, light green, 2 to 5 cm (³⁄₄ to 2 in) long, and very slender; they turn bright yellow in the fall, leaving the pale orange-brown shoots bare until the next spring.
The seed cones are ovoid-cylindric, 2 to 5 cm (³⁄₄ to 2 in) long, with 40 to 80 seed scales; each scale bearing an exserted 4 to 8 mm (³⁄₁₆ to ⁵⁄₁₆ in) bract. The cones are reddish purple when immature, turning brown and the scales opening flat or reflexed to release the seeds when mature, four to six months after pollination. The old cones commonly remain on the tree for many years, turning dull gray-black.
It grows at elevations between 500 and 2,400 m (1,600 and 7,900 ft), and is very cold tolerant, able to survive winter temperatures down to about −50 °C (−58 °F). It only grows on well-drained soils, unable to thrive on waterlogged ground.
The seeds are an important food for some birds, notably pine siskin, redpoll, and Two-barred crossbill.
In autumn, the foliage frequently turns yellow before it falls off.
Larix occidentalis