My mother has a visa to visit the US from overseas. The visa is valid for 5 yrs, multiple entries and for stays of up to 6 months at a time. Does driving to a border town just inside Mexico (say Tijuana) and then returning to the US reset the length of her current stay? In other words, if she were to be here 4 months and then take a day trip to Tijuana, would she be able to stay for 6 more months starting when she returned from Mexico at the border crossing?

I had a friend carrying a Swedish passport do exactly that. he took a day trip and visited Tijuana from San Diego. In his case it did NOT reset the length of his current US stay. CBP treated it more or less as if he had never left the US. He was not trying to reset the length of his stay and was only in the US for a couple of weeks anyway so it was a non issue to him but I'm not sure he could have achieved a different result if he were trying to.

Tijuana is a funny destination. While you are technically in Mexico but you only clear Mexico immigration once you go beyond Tijuana further into Mexico.

I believe the same comments above apply to trips across to Canada.

No it won't "reset" her stay.

Speaking from personal experience, traveling to adjacent countries (Canada and mexico) and islands (Jamaica) doesn't reset your stay - you still keep the same I-94 in your passport and show it to US CBP on reentry.

Some woman from Australia who just transited through HNL on her way to Canada and then went to the states found out the stay started when she transited through HNL and was detained in some ICE lockup.

http://www.deeppencil.com/horror-tra...tion-in-texas/

I think that in order to "reset" her stay your Grandma must hand in her I-94 slip when exiting the US at the border in TJ so when she returns to the U.S. she would need to get a new permit and a new stamp with another 6 months. If she doesn't hand in the slip, immigration at the border will see it and just let her in again without stamping her passport and the original entry date still running.

At Mexico border crossings, is there any US facility at which to hand away an I-94 form? I have walked across the border from TX before, and do not remember seeing any such facility. In fact, nobody was even watching the border from the Mexican side; we just walked right in. (I guess border security is not as heated a political topic in Mexico as it is here - at least re: the US border).

No, definately NOT, land crossings out of the US do not reset this. I believe the Jamaica advice is wrong however as generally flying out of the US WILL reset it.

Nope - this isn't going to work. It's true to say that in order that if she is leaving the US by land and not planning to return during the current stay and depart before the expiration of the current I-94 form, then she must hand it in at the land border before departure to avoid being considered an "overstayer" and having problems the next time she visits.

US Immigration law specifically deals with visits to neighboring countries (Canada/Mexico/Caribbean) and says that visits to those areas do NOT reset the clock, so to speak. Stays in the US immediately before and after to visits to those areas are considered a single continuous stay in the US. Whether or not you hand in the I-94 form upon the first departure is irrelevant.

It will not - at least for the Caribbean. What part of "from personal experience" wasn't clear?

Before continuing with the discussion, why don't her Grandma asks for an I-94 renewal? I believe you should only show financial means to stay in the US and you're on the other side...

I would advise caution with this kind of situation. There are limitations to the B2 visa. You can't just stay for 6 months, leave for a week and come back for another 6 months. I don't think that CBP officers are like this kind of thing. I believe the correct way to handle this is to file for an extension. I found some info here; you can google around for more details.

Not, I believe, if you travel out of the US (by air or otherwise) to the so-called contiguous territories if you are on the visa-waiver program. (This can be a problem, for example, for someone travelling from, say, Europe or Australia to Canada via a US airport and spending more than 3 months in Canada if the return trip also passes through the USA.) The situation might well be different for holders of a multiple-entry US visa, however.

Correct - the clock is only re-set if your stay in those countries exceeds 30 days.