Can I make a leisure trip to California (vacation) in the current covid-19 situation as of 2021, will my quarantine be monitored?

Knowing the st.exchange crowd, I know I am going to get negative votes for this but going to answer it myself anyways as that was the reason I asked this question.

Yes, you can go on leisure trip to California or any other place in the current covid-19 situation, your trip will most likely never be monitored. There is no such system in place yet where they will ask you, where are you going and where will you be staying? Such law enforcement are just never in place and everyone is supposed to observe it on honary basis. So even though there is 14 day mandatary quarantine in place, you can still go on leisure trip within the country, but one thing you will notice, your trip will not be much fun.

Other things

One thing you will notice, your trip will not be much fun esp the travel part, everyone will be wearing the masks and you will come in close contacts with other people (unavoidable) so the danger of spreading covid is real there (to yourself and to others) so it is best to avoid such trips. But once you arrive at your hotel, things would be very much like normal. I did travel and the hotel I stayed in was serving hot breakfast, with everyone still wearing mask all the time except when eating.

Note that you will not be able to get a hotel room directly from the hotel website, because they have mandatory 14 day minimum stay policy hence you will only be using third party websites such as kayak, priceline etc or you can get a travel package from costco etc.

other recommendation is, avoid travelling on long weekends during pandemic, because the plans will be really fully booked, and you will be uncomfortably setting close to each other. The car rental and air fair will also be high, so I would recommend to travel on a normal day just to avoid congestion and be more safe.

Again it is not best to travel and best practice is to be safe at home but then we do go out every day and one get tired staying in same place so if you do decide to travel for some reason, you should be able to without much problems, but it will take some fun from your travel.

Edit: A friend of mine went on honeymoon for 8 days to California, without any problem so really you can go anywhere if you want to. It is just the risk that you take, which is up to you.

The only sensible way to tour California now during the covid19 shutdown is to do it virtually. Find videos that show the places you would visit and watch them instead of taking time money effort and risk to go their physically.

Rent an RV and drive it to the Carolina coast

Since OP's goal is to get some sun, I am proposing a closer destination on the US East Cost. I am not proposing to drive to California. "Carolina" is a pair of states a bit north of Florida.

It's a 13 hour drive. "Oh, that's so much longer than a flight" No it's not. I've crossed the country plenty of times. If you're honest about the "all-in" time from your driveway to the other driveway, it's about 13 hours from Boston to San Diego.

So "drive time" is a wash.

So what are the advantages of the RV?

• It totally eliminates a whole bunch of close contact other than sitting in the airplane proper... including queuing for baggage check, queueing for TSA security, waiting at the airport (which evidence is showing is a real problem), taking public transport within the airport site, waiting at the rental agency -- all places with no consequence for mask non-compliance, so off come the masks and you have a "super-spreader" event.
• It's wheels, directly, which means you can simply go from your driveway to wherever you want to go. The only place you have to stop is gas stations, and having recently crossed the country that way, this can be done contactless if you use a credit card to buy your gas.
• It's easier to roam and explore non-urban destinations, such as a remote beach or trailhead, since you're not forced to be near airports. Getting "out in the country" simply means less contact with people and gives you vastly better choice of safe activities. (and who's kidding who, they're on your bucket list anyway!)
• Carry your own food, so no restaurants. You provision your RV at the start of your trip. If anything comes up, simply do "curbside" at a big-box store where you're already set up. I did exactly that on my recent trip, and it was effortless and instant. (at Target, which really has their act together; this depends on using their app. Downside, Target stores are rare in Trumpland).
• Incremental cost for +1 person is nothin'. So take a partner or podmate.
• Or pet.

My question is, can I take a leisure travel to california by Air out of state?

It's not illegal so you can.

I'm not sure what type of "leisure" you are looking for though. Pretty much everything is closed and in lockdown, so the most likely scenario would be being confined in a hotel room for a 10 day quarantine with take out food and no human contact. That's not my idea of a fun time.

Will my quarantine be mandated?

Yes

Since I will be travelling for few days, my trip would be useless if I had to quarentine myself.

Correct

What is sane advice that I should take?

DO NOT TRAVEL. This is a terrible idea in the middle of a pandemic spike with hundreds of people dying every day in California alone.

How much of risk I am putting myself and others in the current covid-19 situation?

This is a very high and completely unnecessary risk.