Throughout the 1940s and 1950s, it fell into disuse and was forgotten. It became further isolated when 1300 s was paved between 2100 S and 2700 S, cutting it off from the Prison Farm. This marked the beginning of the decline of the park. In 1940, a new Post Office was built, cutting off access to the park from Highland Drive. The completion of Interstate 80 did away with the rest of the Park City rail line in 1967. The 1300 S underpass was filled in when the road was redesigned in the 1960s. Most of the tracks were removed in the 1940s. Douglas to Sugar House also ran through Hidden Hollow. The railroad from Park City followed Parley's Creek through the area.

Subsequently, it was used as a paper mill, a railroad machine shop and offices for the Bamberger Coal Company. The Sugar Mill was built in 1854, though it never made any sugar. Businesses grew up around Parley's Creek in order to make use of the resource. The State penitentiary was located across 1300 E, at what is now Sugar House Park. People could enter the park from both 1300 S and 1100 E. Along with the newly built library, the block became an important community center.

In 1919, it housed a large swimming pool with bathhouses, lighted tennis courts, a baseball diamond and horseshoe courts, a handicraft center and children's playground were also there. The old Sugar House Park was built in 1910 on the block where Hidden Hollow is now: 2121 South 1100 E.

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