J Harlen Bretz (2 September 1882 – 3 February 1981) was an American geologist, best known for his research that led to the acceptance of the Missoula Floods and for his work on caves.

[2] Bretz earned an AB degree in biology from Albion College in 1905, then started his career as a high school History and Physiography (study of the physical features of the Earth's surface)[4] teacher in Seattle.

Bretz coined the term Channelled Scablands in 1923 to describe the area near the Grand Coulee, where massive erosion had cut through basalt deposits.

[8] Bretz published a paper in 1923, arguing that the Channelled Scablands in Eastern Washington were caused by massive flooding in the distant past.

The geology establishment was resistant to such a sweeping theory for the origin of a broad landscape for a variety of reasons, including lack of familiarity with the remote areas of the interior Pacific Northwest where the research was based, and the lack of status and reputation of Bretz in the eyes of the largely Ivy League-based geology elites.

Pardee, however, lacked the academic freedom of Bretz, as he worked for the United States Geological Survey, so did not enter the fray.

As he wrote in 1928, "Ideas without precedent are generally looked upon with disfavour and men are shocked if their conceptions of an orderly world are challenged".

[10] Both Pardee and Bretz continued their research over the next 30 years, collecting and analysing evidence that eventually identified Lake Missoula as the source of the Spokane Floods and creator of the Channelled Scablands.

His post-retirement body of work includes Geology of the Chicago Region (1955), The Caves of Missouri (1956), Washington's Channeled Scabland (1959), Caves of Illinois (1961), and Geomorphic History of the Ozarks (1965), in addition to his 1949 Incomplete Genealogy of the Family of John Bretz Of Fairfield Co, Ohio, with a Partial History of One Line of Descent in this Family.