Coming back down, I considered a side trip to Mt. Disappointment, but, well, it looked pretty disappointing so I took a pic instead and skipped it.
Back at the water tank, I followed the Mt. Lowe East trail to the saddle between Markham and Lowe. I continued on the trail here, branching off a short distance later on the trail to Mt. Lowe's summit. Once on top, I got to share the view with three beauties before they headed off greener summits. I signed the trail register, snapped some pics, then descended again to the saddle between Markham and Lowe. The entire stretch of the trail from the water tank to the summit of Mt. Lowe is in great shape and clear of all offending vegetation.
From the saddle, I followed the obvious use trail along the ridgeline to the summit of Markham. As you might expect, the "trail" conditions here a little different. Although mostly avoidable, there is still a fair amount of PDB encroaching on the path in places and I'd probably wear long pants if I was to do this route again. I suppose I'll know in a day or two how successful I was in avoiding the nasty stuff.
On the summit of Markham, I cracked open my "chick beer," signed the register, took in the views, and then tracked back to the saddle. From there, it was an easy walk back to Eaton Saddle just in time to see a pink moment over the range as the sun went down.
As an aside on summit registers, SG, Lowe, and Markham all had shiny new registers and pens in easy to find canisters. That was an unexpected change from what I've encountered lately. I made sure to do some redecorating of each register in SGDF fashion.
Some pics:

East face of Mt. Markham from Mt. Lowe Road

Entering the Mueller Tunnel

View east from the San Gabriel Peak trail

Summit View East

Close up

Summit View West

Summit View North

Aptly named Mt. Disappointment

View west down Bear Canyon

The 3 Amigos from Mt. Lowe summit- Disappointment (L), San Gabriel (C), Markham (R)

Viewfinders atop Mt. Lowe

The route up the Markham ridge

Massive San Gabriel Peak's south face from Mt. Markham

Mt. Disappointment as seen from Mt. Markham

Redecorated Summit Register atop Mt. Markham.

View south down Eaton Canyon from Mt. Markham

Refreshments are served

Fading light over the eastern range

Into the sunset on the way back down the ACH

City of Angels