As a resident of Isla Vista, there are two important laws you probably hear about quite often, the Noise Ordinance and the Festival Ordinance. As Isla Vista is not a city, laws like this are decided by the County of Santa Barbara, not the residents of Isla Vista. These two laws are often confused, but they are actually two very different concepts. Further, the Festival Ordinance itself needs to be thought of as two separate parts: an overall ordinance on "outdoor festivals" that applies year-round, and a specific set of limitations that only apply during Isla Vista's special events.
The Noise Ordinance can be summarized as: "amplified" noise which is "loud and unreasonable" that is "broadcast outside" of a residence is prohibited at night until 7am, starting at 12am (midnight) on Friday and Saturday and 10pm on all other days of the week. The law goes into detail on the distance from the property line and level of sound required to trigger enforcement, but also explicitly states that enforcement "shall not require the use of a sound level meter" (which makes the definition useless: it is really just going to be officer discretion).
The Outdoor Festival Ordinance, though, is more complex: the first part, and its original purpose, is to generally regulate "outdoor festivals". It states that any "musical activity" whether or not it is amplified where music is either "performe[d]" or "prerecorded" that is held outside of a "permanent" building or installation to which "members of the public are invited or admitted" or which is simply "open to view" which is to be or is attended by five hundred persons or more requires a permit. Permits must be obtained 60 days in advance and carry a number of limitations.
Halloween Festival Ordinance
Some long time ago, it was decided by the County that Halloween in Isla Vista is dangerous from its lack of regulation; however, Halloween is not an event that anyone hosts: instead, it is a number of separate house parties and an associated crowd of people hanging around Isla Vista. As no house party is going to have 500 people in attendance, the Festival Ordinance was considered inadequate, and a second part was added: specifically on Halloween, only in Isla Vista, even small outdoor festivals are simply "prohibited" (as in, there is no permit process).
Originally, this extra rule only applied from October 28th through November 2nd, but over the years the dates were extended by the County to first include October 26th and 27th and then to include November 3rd and 4th, in order to cover the prior and subsequent weekends on years where Halloween fell on a particularly early or late day of the week. (Another change which was made was to limit the consequences of this separate violation of the prohibition of smaller events in IV to an administrative fine, not a misdemeanor.)
Deltopia Festival Ordinance
This year (2015), it was decided that this ordinance should be extended to include Deltopia. Lieutenant Rob Plastino (of the Isla Vista Foot Patrol) also hoped to see the ordinance cover the day (as Deltopia is an event that occurs during the day, not at night), but the text submitted by the County Sheriff and presented in Santa Maria (with no IV community members in attendance) only extended the dates (not times) to include April 3rd through 5th and April 10th through 12th. (They also clarified the administrative fine to be an infraction with associated fee.)
Multiple weekends were covered as the County is afraid that the date of Deltopia might suddenly change; and, of course, the dates of Deltopia would be different on subsequent years. The Board of Supervisors intends to look at this law again during the next year to come up with a more permanent way to cover Deltopia. (They are not certain whether this will even be effective; if it is not, they will just remove the extended dates rather than spend the time to work out a more complex mechanism: this year essentially a test for this law.)
Decisions of Enforcement
While planning for Halloween of 2014, the County Sheriff decided that the dense crowds outside of houses on Del Playa could constitute five hundred people "attending" a festival (assuming music from the house could be heard from outside). This was used to argue that they could apply the normal requirement that outdoor festivals have permits to shut down parties during the day under the threat of a misdemeanor. Sergeant Mark Signa (from the UCSB Police Department) has stated that they will also be taking advantage of this part of the law during Deltopia.
While no warning is required (and despite statements from UCSB that there will be no warnings), IV Foot Patrol intends to give parties warnings. Their goal is to see problem parties shut down, not to see people cited. If someone is cited, it would only be the people running the party. (Attendees who refuse to leave once a party is shut down can also be cited, but this would no longer be part of the Festival Ordinance.) The fine for the nighttime prohibition of smaller events is listed as "up to $500" (but as state law limits the first offense of a county infraction to $100, you should argue).