Complex sentence: They may be off leash on hiking trails on odd numbered days (1st of the month, 3rd of the month, etc.), but must still be leashed in all developed areas, including the road, trail heads, and picnic areas.
Split into simpler sentences: They may be off leash on odd numbered days (1st of the month, 3rd of the month, etc.) only on hiking trails. On odd numbered days dogs must be leashed in all developed areas, including all sections of the road, trail heads, and picnic areas.