I'd definately say that the social life at UC Riverside is what keeps the students together, as well as entertained. At least I could speak on my end, as I was heavily involved in the social scene.
Dorms freshman year:
I lived in East Lothian which was hands down, the best dorms to live in if you want to meet people. Our doors in the dorm rooms remained open, we had talks in the hallway in the middle of the night with our hallmates.. hall activities. Going to the cafeteria to eat was sometimes the highlight of me and my friends day's. Either because we had been so busy study for midterms & writing papers, that that was the only time we could meet over some food. Other times, even if we weren't hungry, we'd go to the cafeteria just to chat and gossip.
Greek Life:
I recommend anyone that wants to become active to join a fraternity/sorority, whether is it Greek or non-greek, or business, all will equally keep you occupied. It really depends on which group you clique with the best.. but Greek life gives you the option to always have something to do.. 6 years ago when I first came to town, I believe the Greek Life was more lively as there were more frat houses.. now it seems there are no official ones.. just houses..
Spring Splash, on campus $10 Concerts:
Take advantage of them!!! Usualy the concerts are 10$ with the student card and have had some pretty big names there.. Xzibit, 112, SNoop, Yellowcard, Jurassic 5...
Dating Scene:
The social circle is quite small, and population as a whole at UCR is rather small.. So word gets out fast.. if you're a private person, better to not date too much on campus.. Gossip is huge as there is not much else to do but for people to gossip.. Thats a big thing to watch out for.. everything and any rumors possible can and will be made up.. so prepare!
Party Scene:
Every night people are partying, mostly at houses, dorms or apartments.. People learn to hustle and eventually master procrastination.. as horrible as that is.. but unless you're in the Bio-med program.. it's not an incredibly difficult school to do well in classes, if you have somewhat of a brain.. Not to say that is a bad thing.. esp if you plan to apply to grad school.. land at least a 3.5 gpa, and you're good to go.
Weekends:
There are not a lot of people left from friday-sunday.. mainly because half the people are locals.. or they'll drive 45 min to go to Orange County or San Diego to visit friends.. but many of the students from Nor Cal may be in town.
Sports teams:
Baseball team was pretty good when I was there, not sure how they are now. The soccer team was pretty good as well. The unfortunate thing about UCR is that there is no football team, nor do we know if they'll ever build one. There are many dance troupes which are highly renown such as 909 to join.. or even to just go and watch at their events.
There are also a lot of activities I wish I had researched about, such as on campus plays, etc.