Leslie Issott Grange was born on 4 March 1894 at Castlecliff, Wanganui, the son of Thomas Issott Grange, a blacksmith, and his wife, Mary Eleanor Conelly. His father deserted the family, leaving Mary to raise her four children in difficult circumstances. Leslie grew up in Waihi, then a booming mining town, where the practical importance of geology would have been obvious. He was educated at Waihi School and Waihi District High School, and then after three years as a dental mechanic's apprentice he obtained a University of Otago scholarship from the Waihi School of Mines.
At Otago he studied under the vastly experienced but prickly professor of mining, James Park, and spent the 1914–15 and 1915–16 vacations working with a mapping party from the Geological Survey Branch of the Mines Department. In October 1916, immediately before completing his BSc under a senior scholarship, he enlisted in the New Zealand Tunnelling Company. He transferred to the Corps of New Zealand Engineers in May 1917 and from September was attached to No 2 Field Company. He saw active service in France, and reached the rank of sergeant. After the armistice he studied geological formations in Britain, France and Germany, and took a course in geology at King's College, London.
In his absence he had graduated BSc in 1917 and was made an associate of the Otago School of Mines. He returned to New Zealand in May 1919 to resume studies at Otago. In December he gained a position as geologist at the Geological Survey. Grange married Bertha Mildred Matthews on 24 May 1921 at Palmerston North; they were to have six children. That same year he graduated MSc with second-class honours from the University of New Zealand.
Working with John Henderson, he carried out geological surveys in the west of the central North Island, and then went on to survey the Motueka subdivision. Here, Grange, Henderson and E. O. Macpherson surveyed over 2,300 square miles of badly mapped, mostly mountainous country in three years, travelling by pack-horse. Where the going was particularly rough they resorted to pacing out distances, compass in hand.
The Department of Scientific and Industrial Research was created in 1926, and that year the Geological Survey, now chiefly concerned with the application of geology to agriculture, was transferred from the Mines Department to become a division of the new organisation. Encouraged by the secretary of the DSIR, Ernest Marsden, Grange directed extensive field explorations of the volcanic zone of the North Island between the end of 1926 and June 1930.
The enormous practical relevance of this work was realised after Grange showed a correlation between the distribution of the Taupo ash shower and the area worst affected by bush sickness. This was a crucial step in solving the mystery of this fatal stock disease, later shown to be caused by a deficiency of the trace element cobalt. Grange's pioneer work in detailed field mapping of volcanic ash showers in the central North Island was recognised by his being made the government volcanologist. From 1932 to 1938 he carried out extensive geological mapping in the South Island, South Auckland, Taranaki, and also in the Pacific islands. In 1935 he received a DSc for his work on the genetic soil types of New Zealand.
In 1936 the Soil Survey became a separate division, with Grange as director, in effect establishing soil science as a distinct discipline. Grange built up the survey from scratch, with staff recruited from a range of disciplines. In 1945 it was reorganised and named the Soil Bureau. Despite the increasing importance of the work of the bureau it had no permanent home, existing in pockets in several old buildings around Wellington. Grange secured land at Taita, but the Soil Survey building was not opened until 1962.
By the early 1940s attention was increasingly being focused on the problem of soil erosion. A royal commission on sheep farming, which finally reported in 1949, saw farmers in deep conflict with conservationists over the control of the use of private lands. Grange had become personally concerned with the problem of erosion and presented a detailed paper for the conservation side. He continued as director of the bureau until 1952, when he returned to the Geological Survey to take over as director.
In his four years at the helm Grange managed to put the administration on a sounder basis, after the laissez-faire directorship of Montague Ongley. He continued his interest in volcanology; his DSIR bulletin Geothermal steam for power in New Zealand laid down the programme which resulted in New Zealand's world leadership in geothermal technology. He was also involved in the excitement over uranium finds, publishing Prospecting for radioactive minerals in New Zealand (1954) and helping to investigate claims on the West Coast. He retired in 1956, and for the next 10 years acted as a geological consultant, working in New Caledonia, Fiji and the Philippines as well as New Zealand.
Leslie Grange served on a number of committees related to his work, including the central standing committee on soil conservation. He was a fellow of the Royal Society of New Zealand and chairman of the Wellington branch. After retiring he was a director of the Development Finance Corporation. He published more than 50 papers in a variety of journals, including the New Zealand Journal of Science and Technology and the Transactions and Proceedings of the Royal Society of New Zealand. He was appointed to the Imperial Service Order in 1958.
A tall, lean man who wore glasses from a young age, Grange was most at home in the field, and was in later life to pour contempt on laboratory researchers who seldom pulled on tramping boots. He is remembered by colleagues as shrewd and modest, with a 'quizzical manner and dry humour', and as revelling in the appearance of a loveable rogue. Adapting to home life with a large family did not come easily, and his children remember his insistence on complete silence in the house, to the extent that he would eat separately. Despite being a meticulous scientist he filled the house with a jumble of rock samples. He was an ardent photographer and built himself a darkroom at the back of the house.
Bertha Grange died in November 1943, leaving a still-growing family. On 31 May 1946, at Kaiapoi, Leslie Grange married Mary Luxton Brown, a librarian, with whom he had a daughter. The marriage was not a success, and a divorce was granted on 24 November 1954. At the age of 72 he married Indus Harrison Clark (née Fantham) in Auckland on 24 February 1967. Leslie Grange died in Wellington on 6 October 1980 survived by his wife and children. He is commemorated by the Grange Building, formerly part of the Soil Bureau in Taita.