Circled in red in the photo below, three surveyors with minimal safety gear are preparing anchorage lines for an aerial tram in Boulder Canyon.
While workplace safety is a legal obligation with all forms of employment in 2018, such concerns were rarely considered in 1931. Case in point is this photograph of these surveyors nonchalantly triangulating points along the sheer cliffs of the canyon without harnesses. OSHA (Occupational Safety and Health Administration), the institution in charge of the creation and enforcement of workplace safety regulations, would not come about until 1971, forty years after this photograph was taken.
NARA Series: Boulder Canyon Project Series, 1948-1966. Record Group 48: Records of the Office of the Secretary of the Interior, 1826-2009. National Archives Identifier: 2292774