As others have suggested, it sounds like there is something providing much better drainage under that spot--could just be a column of sand or gravel rather than a void. How big is the spot? A foot or two, 10 feet? 30 feet? In my area it is not uncommon to have subsurface gravel or sand or old stream beds that are only a couple feed wide but will dry incredibly quickly after irrigation--one spot will be wilting, 5 feet away the soil can still be a little overly wet from the last irrigation. Another possibility is that something was dumped on the soil at some point in the past. Oil? gasoline? Salt? and it is still in the soil, repelling water or making it unavailable to the plants and causing your problem. If the concentration was high enough to affect the added soil of a raised bed, I would think you would notice its presence, though.

I've seen waxes given off by the trees mentioned. Otherwise when the conifers are still present a planting area can be dusty because they may use their crown structures to divert water away from the trunks, resulting in persistent dryness beneath their canopies. But local soils can be dry to some depth in October just because it stops raining in July and there isn't enough precipitation to compensate again until the hammer falls in November - the stormiest month of the year. If a body doesn't water enough to compensate and the planting is not made on a retentive soil or a site that tends to remain more moist for other reasons then by this time of the year they will be finding some quite dry dirt when they dig around.

Christina, Those feeder roots (the smaller ones) are just that. If they're not healthy, they should go. While I agree most of the time with xero's advice (he's a much better grower than I am), IME Aloes respond with outstanding growth given a proper root whacking, particularlay when they've been underpotted as yours has been. Besides, it doesn't really want a large pot, at this stage, large enough to accomodate your present root mass. Take off half of those and put into a pot appropriately sized for the future root ball after it's been cut. You'll then, in a year or so, be able to upsize the pot when you repot next, having a plant that has overgrown (but not severely-restricted roots like the plant originally came with) but healthy roots, probably just popping the whole mass into the next size (or two) of pot.

There are a variety of factors which may have contributed to your plant die off. The lack of humidity is undoubtedly an issue. Your plants may be able to adapt to such outside, but it would take time. During that time, they might need watering more frequently and sheltered from direct sun particularly during the afternoon. With the plants you lost after placing outside in CA ---- did you take the time to harden them off? From what you said in your OP, I got the impression that you did not. In which case, it is not surprising that they got fried. If the plants were originally indoors or grown in a greenhouse with shade cloth, they would not be used to full, unfilter direct midday sun. Setting them out in full sun without hardening them off would be comparable to taking a fair skinned person who has spent the winter indoors and taking them on a 5hr midday desert hike in shorts and a tank top with no sunscreen. At best they will likely have severe sunburn/"sun poisoning " (likely requiring hospitalization). Media containing peat is avoided by many cacti/succ growers. It tends to hold too much water too long but, perversely, when completely dried out is hydrophobic and is incredibly difficult to quickly remoisten. Sphagnum is also generally avoided by cacti/succ growers due to water retention and how quickly it can break down. (Although, in your low humidity circumstances, perhaps it could have its place.) When you repotted, did you remove the old soil? Many commercial BBS suppliers do use mixes with a high % of peat. BUT their conditions and watering practices are, in all likelihood, radically different than yours. IF they were using such a media, and IF you did not remove it before potting the plants up, then there is yet another issue. It is completely possible that the peat "ball" around the roots completely dried out becoming hydrophobic. A light watering would moisten the exterior new soil but but not the peat ball where the roots actually were. If you did remove the old soil, did you give the plants time to grow new roots before giving them full sun outside? (Goes for CA and NV.) Removal of old soil inevitably causes damage to the fine roothairs which are responsible for water uptake. It takes a little time to grow new ones. During such a time, the plants would need to be coddled a bit (no hot direct sun, for example).