Sisters View is 1.8 miles RT hike of about 600 feet gain or, perhaps less if your vehicle is capable.
This summit is near several others, Gray Butte-W7O/CE-180, Grizzly Mountain-W7O/CE-135 and Pine Ridge-W7O/CE-208.
Depending on how far you choose to drive, Gray Butte will be a 1.4 mile road hike (OW) with about 1200 feet gain. There's another summit that could add another two points with 1.8 miles of hiking. Although I was thinking that the road might require high clearance, a Prius drove up after me - so know your vehicle.
Pine Ridge is a steep hike of a little less than one mile (OW) and 800' vertical, close to Gray Butte-W7O/CE-180 and Grizzly Mountain-W7O/CE-135 so you might consider doing other peaks in the area.
Lookout Mountain is a lovely hike of about 1.75 miles (OW), close to Round Mountain-W7O/CE-045 so you might consider doing both of those peaks. Note that there are MANY Lookout Mountains - this one is east of Prineville.
Round Mountain is a road hike of about 2 miles one-way and 1000 feet of gain. It's close to Lookout Mountain-W7O/CE-039 so you might consider doing both of those peaks.Note that there are FIVE Round Mountains in Oregon, with one in CE near Lakeview. This is the Round Mountain east of Prineville.
Ochocco Mountains High Point could be considered a drive-up summit...for some vehicles. Although most of the way is paved, your low clearance passenger vehicle will have problems with the road in places where you can't turn around. A quarter mile of walking to the summit is recommended - it's a neat spot.
About 30 miles east of Prineville on Highway 26, turn north on Forest Road 27. This may be described as Grant Springs Road, or Summit Road, depending on your resource. This is near milepost 49.
Vinegar Hill is located in Oregon above the Middle Fork of the John Day River near Bates State Park. The veiws from the top are spectacular. It is easy to find as there is a sign from the Middle Fork road pointing to forest road 2010. It reads 13 miles. The first six of those are good gravel accessible to any car. The next six are rutted and rocky and require a high clearance vehicle. The last mile is available to a 4x4 in late summer or early fall. When we were there on July 1st the road was blocked by snow, so we walked the last mile and 650ft of elevation.
My son and I did this activation. The starting point for our hike was the intersection of FR 5603 and the Pacific Crest Trail. We parked at this location and started walking down the PCT which was adjacent. We found no trail to the summit so we started bush whacking. It was not too hard. After about an hour, we made the summit.
Chase Mountain is in the Blue Mountains of southeastern Washington near the town of Dayton. There is no trail to the summit, but you can drive right into the activation zone. Park at the bottom of forest service road 6437 for a 2.2 mile walk or drive up to the top and walk out and back in as I did. There are a few places at the top to pull your vehicle off the road.
Oregon Butte is the highest peak in the Blue Mountain Range of southeast Washington State. There is a lookout up there which should be staffed by early July.