Jeff,
This was a super-regional qualifier. They had well over 200 (~240) contestants for 9 places and two alternates. The tournament had to be held over two days.
That is because they chose to do it that way.
When the Amateur was at Oakmont, we chose to have 3 qualifiers rather than try to run on giant one. We had 234 players (78 at each).
When the US Amateur was held at Pumpkin Ridge in 1996, the OGA had one qualifier in one day with 192 players at two courses. You played one in the morning and one in the afternoon.
The Georgia State GA usually has one big two-day qualifier for the US Am, but has a cut after the first day so only those with 7 shots of the lead (or some such number) get to come back.
My personal preference is for how we did it 2 years ago. With a huge field, you run the chance of bad weather really messing you up. As it was, we had bad weather at one of our sites and had to go to a second day for that one, but otherwise it worked great.
This year we had 2 qualifiers with a max of 78 at each one. We got 69 at each site. I'm glad we didn't have to do a 138 player qualifier over one or two days. Of the 6 players who qualified, 3 are mid-ams so playing 36 in one day didn't hurt too much here.
The USGA usually prefers the 36-hole qualifiers to be held on one day, but will allow other formats such as Philly or Georgia use.