The Crescenta Valley extends eastward from the Los Angeles City communities of Sunland and Tujunga through a portion of the City of Glendale and the County territories of La Crescenta and Montrose to the incorporated city of La Ca–ada Flintridge. Sunland was annexed to the City of Los Angeles in 1926 and Tujunga in 1932. The remainder of the Crescenta Valley stood as County territory until January 1952, when the City of Glendale annexed the strip which included the commercial section of Montrose and extended up into the Verdugo & San Gabriel Mountains. The communities of La Ca–ada and Flintridge joined together in incorporation in December 1976, while portions of La Crescenta and Montrose still remain as part of Los Angeles County.
After the disastrous flood of 1934, the U.S. Army Corps of Engineers and the Los Angeles County Flood Control District embarked upon a major construction of dams, channels, debris basins and continued efforts to control erosion. Major fires swept the La Crescenta area in 1933, 1964 and 1975. A major earthquake in 1971 left La Crescenta with a minimum of damage, but several old commercial buildings had to be demolished.