In 1943 a consortium of contractors including Morrison - Knudsen began new construction on the dam ultimately raising its height to 475 feet ( 145 m ) .
Morrison - Knudsen had previously participated in construction of Hoover Dam .
In 1943 a consortium of contractors including Morrison - Knudsen , which had previously participated in construction of Hoover Dam , began new construction on the dam ultimately raising its height to 475 feet ( 145 m ) .