Wife's B-Day, wants to hike somewhere cool, I'm thinking Slate Mountain Trail but am open to anything we can drive to, hike, then return to the Valley in a day trip.
Depends on what the definition of easy is. I did Kendrick Peak a couple months ago. 9 miles out and back, but if that is too far, just go halfway and turn around.
The real rock candy mountain of hiking information is alltrails.com. Search for easy trails around Flagstaff and you will get a ton of choices.
The See Trail out of Christopher Creek is nice. You can actually take it all the way to the 300 road which we did a few years back. Very pretty and water along the way.
The request is a bit vague. Don't know how many miles you consider easy or what you definition of northern AZ is, I would consider that Jacobs Lake area. But I am going to guess that meant north of the valley in cooler weather. I have always enjoyed the Horton Springs hike.