Heiðmörk was proclaimed a municipal conservation area of Reykjavík in 1950. It is located southeast of Elliðavatn, Iceland, and is about 6 miles (9.7 km) from the city of Reykjavík. Its name is derived from its namesake in Norway, Hedmark (Icelandic: Heiðmörk; both derive from the Old Norse Heiðmǫrk), an area with deep forests.
The total area of the conservation area is 3,200 hectares (7,900 acres). It is a popular recreational area in Iceland. Heiðmörk is where Reykjavík's water reservoirs and drinking water wells are located.
Rauðhólar are a notable natural formation of Heiðmörk, a cluster of red coloured pseudocraters.
More than 4 million trees have been planted since 1950 and the existing vegetation has thrived since the area has been fenced off. The most prominent of the 26 species of trees at Heiðmörk is the Sitka Spruce and at least 150 wild flower species have been counted.
More than 60 species of wild birds have been counted, especially around Elliðavatn and Myllulækjartjörn.
Tree planting in Heidmork began in the summer of 1949 in so-called Teygingar on the heathland above the old farm of Elliðavatn (Elliðavatnsheiði). There were planted 8.000 plants of Scots pine (Pinus sylvestris), 500 of Norway spruce (Picea abies), and 500 of Sitka spruce (Picea sitchensis) which now forms a part of the woodland in Heiðmörk now known as Undanfari. Scots pine is scattered near Undanfara and on Elliðavatnsheiði, and probably some can be traced back to the first planting in Heiðmörk. It is worth mentioning that the spring of 1949 was one of the coldest during the 20th century. The forest in Heiðmörk now covers 820 ha of Conifer and 650 ha of Birch in gross profit. Reykjavík Forestry Association has supervised and managed the afforestation in Heiðmörk from the starting point. Reykjavík Municipal Work School has done an invaluable work on the premises and the teenagers continue their work in the summer.