The Pinnacles, Limestone formations in Nambung National Park, Western Australia.

The Pinnacles are thousands of limestone pillars rising from yellow sand in Nambung National Park, Western Australia. The tallest reach 3.5 metres; some are column-like, others short and tombstone-shaped. Many show cross-bedding where the angle of deposited sand changed with the wind, and mushroom tops form where a harder calcrete cap protects softer limestone below.

The Pinnacles are limestone formations in Nambung National Park, near Cervantes. The limestone originated from seashells broken into lime-rich sands that were blown inland to form mobile dunes. How the pillars themselves formed is debated: one theory holds they are dissolutional remnants of Tamala Limestone; another that tree casts in coastal aeolianites became groundwater conduits precipitating calcrete; a third that plant roots concentrated calcium into calcrete. The area was gazetted as a reserve in 1967 and combined with two adjacent reserves to form Nambung National Park in 1994.

The Pinnacles Desert Discovery Centre opened in 2008 and explains both the natural processes that formed the limestone pillars and the biodiversity of Nambung National Park. The park draws about 150,000 visitors a year. The name Pinnacles comes from the column-shaped formations, which stand taller than they are wide, unlike the shorter tombstone-like ones.

A loop road runs through the pinnacle field, with parking bays where you can leave the vehicle and walk among the pillars; a marked walk also crosses the sand. There is no lodging or camping inside Nambung National Park, so base yourself in Cervantes. Days are mildest from August to October, when wildflowers and wattle begin to bloom.

The pillars are not uniform: many show cross-bedding, where the angle of the deposited sand layers changes sharply, recording shifts in the prevailing wind during the formation of the limestone. Others carry a harder calcrete cap, so the softer limestone beneath erodes faster and leaves a mushroom-shaped top.