Work on the Boundary Channel Bridge began in the spring of 1929, but immediately ran into problems. An unstable rock shelf thick lay under the western abutment of the Arlington Memorial Bridge. This "rotten rock" had not been revealed by borings two years earlier, but now came to light as construction began on the Boundary Channel Bridge. Additionally, a thin layer of sand and gravel was discovered lying atop the bedrock of the eastern abutment of the Boundary Channel Bridge. Both obstacles had to be removed before construction could proceed further. By June 30, 1929, the Arlington Memorial Bridge's western abutment was finished (except for exterior masonry facing), and many of the concrete columns for the Boundary Channel Bridge were also finished.