A good, flat trail but probably crazy hot on the wrong day.
From the parking lot at the Old Mission Dam, take the Oak Canyon Trail along the creek until you see a sign for the Grasslands Loop Trail. Take a right and then a quick left. You'll head slowly uphill and north for 1/2 a mile until you can turn right. Cross a large open field and when you meet up with the Spring Canyon Trail turn right and then right again. Shortly, you are back where you started.