As getting adjusted to squatting again, might consider bwt squats only; Hindu, military style, etc.. Doing 20-30 easy reps of 3 sets to get use to a full ROM. This should not be overtaxing, so squatting 5 days in a row might be suggested, with the last two day adding a 100lbs on a bar for a couple sets of 20 reps of regular squats. All to get the legs programed to the feel of squatting again. Than take three days off of squatting and begin a more serious attempt of heavier weighted squats next workout. Something like reps in the 6 to 9 range, with 2 or 3 sets each.
I think way too much importance is placed on DOMS (Delayed Onset Muscle Soreness). Increased blood circulation is know to flush and return the muscled area to a readied state for further workouts, reducing the affects of DOMS. That's why the above suggest of working light squats for 5 days in a row. Along with heat lotions, pads, etc. Deep tissue massages have given very rewarding benefits to many athlete's.
Might suggest, along with regular BB squats, Step-Up with holding DB's in each hand for added resistance. Would suggest a BB across the back but some have a question of balance this way, but do whatever feels best for you. Want to work each leg individually to insure equal strength, balance and development. Step-ups also influence the hams and hips greatly. Have the box/bench/platforms around knee height or a bit lower depending on body type. Might find than having a focus on Step-Ups will have a greater benefit than regular squatting does. Even working the hams/lower back can be a great aid, as with GoodMornings, SLDL's, etc. Simple leg curls also. Try working to focus on the legs twice a week. Your not going to need a lot of sets, just brief and to the point leg training. Most athletes find Step-UP a great help in their chosen sport.
Going to get a continual blood pump to the legs with serious MTB biking, also with short sprint racing, so the legs should increase in denser muscle tissue. Tension is usually on the legs during the duration of MTB training. And more blood builds more muscle tissue.
Good Luck.