Descriptive statistics
COVID-19 experiences, stress, and sleep. Participants’ reported experiences with COVID-19 at baseline are shown in Table 
COVID-19 related experiences of participants in Study 1Was not able to work due to COVID-19 illnessImpacts no participants endorsed across Studies 1 and 2 were: increased childcare costs, not enough money for rent or medications, no regular place to sleep.When examining inter-correlations between key behaviors of interest in the analytic sample, hiking frequency, stress, and sleep were generally linked as expected, although these links tended to be stronger at later study time points. Greater hiking frequency was linked with more hours of sleep per night at midpoint at a trend level (r = 0.31, p = 0.06), and this relationship was statistically significant post-intervention (r = 0.43, p < 0.01). There was no association at baseline. Greater hiking frequency was linked with less stress post-intervention (r=-0.36, p < 0.05). The magnitude of this correlation was in the same direction at the other time points but not statistically significant. These relationships were generally consistent with and without an adjustment for study group and when including all enrolled participants.Intervention implementation. Overall, 22 of 26 (84.6%) participants randomized to the intervention group signed up for the Western New York Winter Hiking Challenge. Of those who signed up, 45.5% reported completing at least 1 challenge hike, and 18.2% completed the challenge by completing 8 hikes. Those completing challenge hikes at midpoint reported hiking with spouses/partners, children, other family members, and friends, and generally found hikes to be enjoyable and of an appropriate difficulty. At post-intervention, results were similar, with full intervention implementation data at post-intervention shown in Table 
Intervention implementation and acceptability in Study 1Completed challenge hikes with(select all that apply):0.0% not enjoyable, 20.0% moderately enjoyable, 80.0% very enjoyableWe were able to confirm that one control-group participant completed winter challenge hikes via records from the hiking challenge (i.e. this participant was randomized to the control group but found out about and engaged in the hiking challenge on their own). After post-intervention, when free registration for the Western New York Summer Challenge was provided to the control group, 12 control-group participants signed up for this hiking challenge. In addition, 5 intervention-group participants signed up for the Summer Hiking Challenge on their own, indicating maintenance among half of the intervention-group participants who were active in the winter challenge.