Over the Rainbow 5.10a
Apron, The Chief
About the Climb
Over the Rainbow is a fine moderate slab climb and a good practice route for the steeper Apron slab routes. All the slab sections are bolt protected, but you still need a small rack for a few other sections.
The route shares the start with the very popular Diedre (5.8) and Banana Peel (5.8), so don't freak out if you see many parties when you arrive at the start of the route. Should there be other parties waiting for Over the Rainbow, the old-school Sparrow (5.9+) is a great alternative.
Although the top part of the route has great climbing, the Sickle Arete Finish (5.9+) is a fun alternative finish if you are stuck behind a slower party. It climbs the arete to the left of Over the Rainbow and joins Diedre (5.8) on the last pitch.
The Apron has a high density of routes, so there are plenty of options for combining Over the Rainbow with another route. Instead of hiking and scrambling up to the Diedre Ledge, you can climb The Bottom Line (5.9), which is a short slab route that starts right off the trail along the base of the Apron, and finishes at the right end of the Diedre Ledge. It is a great warm up for the slightly steeper slabs of Over the Rainbow.
From the top of Over the Rainbow there are various other options if you want to add more pitches of climbing to your day. If you feel like climbing more slabs, you should go climb one or more of the Upper Apron routes. The bolts on these routes are a little more spread out, but you should be fine after the 'warm-up' on Over the Rainbow. If you descend along the Broadway Ledge towards the forest, you will pass directly below the Upper Apron. By combining The Bottom Line (5.9) with Over the Rainbow and an Upper Apron route, you can climb more than 10 great slab pitches in total.
If you want to climb something else than a slab, there are plenty of other options as well. The Boomstick Crack (5.7) starts only a few feet right of the top of Over the Rainbow and traverses along an amazingly thin flake. Alternatively, you can move left along Broadway to the nothern end of the Apron and climb the Memorial Crack (5.9). From both routes, you can continue up and climb either the Squamish Buttress (5.10c) or Ultimate Everything (5.10b) all the way to the top of the Chief. If you combine The Bottom Line (5.9) with Over the Rainbow and some of these extensions, you can climb up to 20 pitches in total, all the way from the base to the summit of the Chief.
Many of the routes on the Apron have some slab climbing sections. Sparrow (5.9+) is just to the right, and is quite similar to Over the Rainbow, although the protections is a bit more sparse. The Upper Apron also has a few short slab routes in the 5.8-5.10a range, which can be easily added to your day if you climb a route on the Apron, and descent by the Broadway Ledge. Another short slab route is The Bottom Line (5.9), which starts direclty off the trail along the base of the Apron, and finishes at the right end of the Diedre Ledge.