4 X 1 mile at tempo effort. I ran by feel (but recorded HR) and kept the effort relaxed and fast. I dipped below 8000ft altitude only a couple of times.
Splits and average HR (my lactate threshold HR is ~175-176 right now)
5:47 HR 162 (lots of downhill)
5:56 HR 164
5:35 HR 166
6:00 HR 169
The original plan was to rest 1:00 between these but it was 16 degrees and windy and I froze on the first rest interval so I cut the next two to 11" and 22". A picture of the course profile is below, it's the absolute flattest course I have. I wouldn't call that hilly (it looks worse on the profile than it actually is) as it only had 435 feet of climbing in the 4 miles. Overall PE was marathon effort down to 1/2 marathon effort but the Governor joined me for the last 200 meters which finished up a pretty steep hill... he had some pretty convincing ideas as to how to finish but I was able to politely tell him to piss off.
And on my cool-down home I found this sticking out of the ground. It's almost perfectly round and I think is carved from marble or some kind of stone.