Where I run

Pineridge Natural Area
Size: 618 acres
Key Habitats: Shortgrass prairie, foothills shrubland, foot hills pine forest.
Adjacent to 40-acre Dixon Reservoir.
Description: The site contains a large prairie dog colony. Mule deer are common in the forest, especially in winter. Red-tailed hawks nest in the pines. A variety of foothills birds and small mammals are found here. The rare Bell’s twinpod grows on the ridge on the east side. The adjacent reservoir supports migrant waterfowl and other waterbirds. Pelicans, ospreys, and bald eagles use this natural area. Mature cottonwoods and willows provide habitat for migrant songbirds, including vireos and warblers. Over 150 bird species have been seen here. Features: Parking lots at County Road 42C and at the east end of Horsetooth Road; access from Foothills Trail; 3 miles of soft-surface trails; restroom.

Where You Are Likely to Encounter Rattlesnakes:
Rattlesnakes like rocky outcrops, rocky stream courses, and ledges. They may den in mammal burrows, rock crevices, or caves. They may be on the trails – either going across the trail as they move from one place to another or laying on a paved trail to soak up warmth. They also may be in grasses and other vegetation beside a trail.

Oh yeah...and there is this...
There are several Fort Collins natural areas where you are likely to encounter rattlesnakes:
Pineridge Natural Area. (There is an emergency telephone at the Dixon Reservoir parking lot.)