Toms thumb is a great trail to go on in the north valley and is approximately 2 miles each way. The first journey is getting to the parking lot where you will be oscillating back and forth as the hills make you go up and down. After the first flat portion of the hike, you will be walking up switchbacks for days it seems and will definitely feel it in your thighs. It is probably just about as strenuous as camelback with all the switchbacks and just because the distance the switchbacks cover is much greater while camelback is more steep and much shorter hike.
Jacket would be recommended in December as some parts can get a little windy. I would definitely recommend bringing at least a liter or two of water depending on what the weather is like. I would definitely come by again!