Moreau Lake State Park is a popular spot especially in summer, known for its swimming lake, camping, and mountain biking. Located 11 miles north of Saratoga, the park is also terrific for trail running, with 15+ miles of trails, and several marked loops. This trail map has excellent information on the various options. A loop around the lake on the Nature Trail (turquoise on the map) is 3 miles, mainly wooded with occasional lake views. There are also some more rugged trails that form even longer loops, the most ambitious of which is the nearly 6-mile Western Ridge Trail.
Great spot in summer for a run and a swim!