That herd is a culmination of several area herds losing a few animals over the years to form what you see now. The Tenino herd, specifically the ones that ran behind the Alpaca Farm (previously owned by Dan Agnew as Dan-Dar Farms) had several cows and a couple of small bulls that ran the gauntlet over I-5 and ended up over there an up into Capital Forest. Others came from the Lincoln Creek herd as there was a bull that I had seen for a few years that ended up over there. Also, there was a small band of elk running around near the E/D Lines in Capital Forest over quite a few years however there numbers were kept low. This was mostly due to them occasionally crossing over into tribal ground near Gate road that they were getting mowed down by tribal hunters in the fields just off Hwy 12 near the Black River. The other problem is they were just flat out being run around by a few dedicated hunters and quad riders. That area off 113th that they reside in now was made a preserve and since then tend to live there, occasionally sweeping north as far up as almost Black Lake Blvd, but typically stick to private ground. Some decent genetics in there however yes, that herd is rampant with hoof rot, which is a passion/hate issue with me so I will refrain from giving my opinion, lol. Last year the Thurston County SWAT team snipers were used to take out 2-3 'bad' animals. Its a closely watched herd by neighbors.....every year someone tries to sneak in there for either sheds or a chance at taking a shot at one of them and usually they are caught. Between a landlocked preserve by privately owned property owners which closely watch that herd its impossibly for even a calf to be born and not be noticed. Its awesome to see that herd growing, but the question will be to see where some go from that spot if they are forced out by numbers.
To answer your question Screamin', there about 6-8 bulls that are ALWAYS there along with a fair amount of cows. Most of the cows hang out just west of that field into private ground. Some of the younger bulls come from Capital Forest and come down for the September festivities. Every year around winter it seems 1 or 2 young raghorns get tatered by motorists on I-5 too on their attempt to head East. But yes, most of locals either from the west and north directions. It seems the other band of elk on the growth is just to the north of there that run the power lines up to Mud Bay road and also private ground...Im sure they are some of what you've been seeing there as well.
Anyway...that's about the only history I know of that herd and mostly due to watching them for a lot of years...I think its kind of a cool location as I can take my kids out there at most any given morning and at least see a few of the herd members.