1.0 hr
Off of E Mesa Fire Road, you'll find the well-marked trail that begins just up road from where Lower Descanso Creek Trail ends. The trail starts relentlessly uphill at a very even but not overwhelming incline. You slowly gain a commanding view of the creek and some of the open grasslands. After 1.5 miles just when the trail begins to flatten out, there is the well-marked Oakzanita Summit Trail on the right that heads to the Oakzanita Summit which is probably why you're here anyway.
The start of the Upper Descanso Creek Trail is marked by this sign.