Yes it does seem a bit small. The only other beaver exhibit in Arizona that I know of is at my local Arizona Sonora Desert Museum, which has a very large pond and underwater viewing. The beavers there, though, are strictly nocturnal so the only time I have seen them in the pond is during their Saturday night openings. This beaver (at Bearizona) was semi-active when I walked by, though it was just before sunset so maybe that helped?
I agree beaver tend to be most active early in the morning and towards dusk, though I have occasionally seen them active in the middle of the day. I think facility care schedule affects their activity to a fair degree.
@Arizona Docent@Great Argus I have been to 4 or 5 collections with beavers - I've seen them maybe once! Keep in mind that two of those collections I have visited 5 times!