Research has found that human-caused noise can detract from the quality of the visitor experience in national parks and related areas. Moreover, impacts to the visitor experience can be managed by formulating indicators and standards of quality as suggested in park and outdoor recreation management frameworks, such as Visitor Experience and Resource Protection (VERP), as developed by the U.S. National Park Service. The research reported in this article supports the formulation of indicators and standards of quality for human-caused noise at Muir Woods National Monument, California. Phase I identified potential indicators of quality for the soundscape of Muir Woods. A visitor "listening exercise" was conducted, where respondents identified natural and human-caused sounds heard in the park and rated the degree to which each sound was "pleasing" or "annoying." Certain visitor-caused sounds such as groups talking were heard by most respondents and were rated as annoying, suggesting that these sounds may be a good indicator of quality. Loud groups were heard by few people but were rated as highly annoying, whereas wind and water were heard by most visitors and were rated as highly pleasing. Phase II measured standards of quality for visitor-caused noise. Visitors were presented with a series of 30-second audio clips representing increasing amounts of visitor-caused sound in the park. Respondents were asked to rate the acceptability of each audio clip on a survey. Findings suggest a threshold at which visitor-caused sound is judged to be unacceptable, and is therefore considered as noise. A parallel program of sound monitoring in the park found that current levels of visitor-caused sound sometimes violate this threshold. Study findings provide an empirical basis to help formulate noise-related indicators and standards of quality in parks and related areas.