Are immigrants the cause for poverty in the US, esp in CA?

The American Progress is using a standard poverty measure which is the same across all states.  But the supplemental poverty measure takes into account cost of living for the location.  And in that measure, CA is much higher.  Here is a link with that data: https://www.census.gov/library/stories/2024/09/supplemental-poverty-measure-states.html

There is important nuance in understanding these issues.  Some things to consider:
1) People in poverty are not only immigrants.  Immigrants do have a higher rate of poverty, but still 12% of native born citizens in the USA are living in poverty.  That's a lot - more than 30 million people! The number of Americans living in poverty is far higher for native-born Americans than it is for immigrants.  Similarly, there are far more white Americans living in poverty than there are of other races.
 
2) Of those who cross the southern border, there are very different groups crossing.  Many have legal permission to cross as workers.  And the US and especially CA need these workers mostly as a result of the 1965 immigration law. Before 1965, the US (under the Johnson-Reed Act) would set limits by country of who could emmigrate here. This meant that there would be an allotment of a certain number, for example say 25,000Germans in one year, to come to the US. The result was that low skilled and cheap labor from many of these countries could come to the US. After 1965, the law changed to focus on skilled labor that is desirable - so , for example, nurses, doctors, engineers, etc... without respect to their country of origin.  The result was a far more ethnically and racially diverse country with LESS social class diversity.  This meant that after 1965, the cheap labor that used to immigrate to the US dried up.  Many US businesses that relied on cheap labor such as restaurants, farms and factories turned to labor from Mexico and Central America to fulfill the demand. Without these cheap workers, our economy would drastically change.  Most of these workers are allowed in legally as temporary workers.  The economy needs them.
 
3)Another type of immigrant coming to the US are refugees.  Refugees are from places designated as disaster areas.  For example, in the Sudan, there has been an ongoing civil war that has displaced hundreds of thousands of Sudanese people.  These people are officially refugees designated by the United Nations and other international organizations.  These people agree to be resettled around the world.  The US is just one country that resettles refugees.  Refugees are flown to a country and then set up in an apartment and volunteer organization help them find education and jobs. Usually, the rent for living expenses are donated for the first few months until the refugees can find a job and pay their own living expenses.  And they must reimburse the government for the price of their flight to the US.  These people are here legally and they have fled civil war, genocide and devastating circumstances. 
 
4) Another group that comes to the US (which is the group that I think you are referring to) is asylum seekers.  Asylum seekers are also governed under international law. A brief background: during WWII, thousands of Jewish people fled the holocaust in Europe.  Many were turned away from countries who said, "sorry you don't have the paperwork to enter our country."  One example is the boat named St Louis which had 900 Jews on it.  It was refused by the US and sent back to Europe where most of the people were killed in the holocaust. So, new international law after the war said that anyone who shows up at your port of immigration must be guaranteed a hearing to determine if they should be allowed asylum.  The US has not updated its immigration laws in decades. This has been especially salient the last 10 years or so as the rise of social media has shaped the global landscape in 2 profound ways.  First, social media has been used to destabilize the global order - starting with Syria and the Arab Spring to Myanmar's Rohinghi genocide to Haiti and Venezuela. All of these countries have sent thousands of asylum seekers in search of help and stability.  The second way that social media has added to the crisis is with information.  It has allowed these asylum seekers to find paths to security - namely by flying to Columbia and then following a route from there through Central America to Mexico and up to the US border. As more have arrived, the US system is not staffed or funded to process the many who have come here. Real reform needs to happen to shore up the system to deal with surges like this. 
 
5) None of the people I have mentioned above are immigrants who are sneaking over the border without processing or inspection.  This group is often called EWI or entry without inspection. The number of EWI immigrants in the US peaked in 2007 but relative to the total number of immigrants in the US, the number of EWI is quite small - estimated around 300,000 per year.  This is different than the people who might come to the US without paperwork but are seeking asylum, or those who enter the US legally but then overstay their visa.  When you add up all of these groups and put them into the umbrella term of "illegal" this group is around 10-11 million people currently in the US.  Often politicians and news media conflate all of these groups by using an amorphous term like "migrants" or "illegals".  This clouds reality and doesn't help the public understand the specifics of what is going on.  The PEW has a detailed explanation of EWI immigrants here.  But what we should be careful of is understanding the difference between immigrants, refugees, asylum seekers, migrant workers, EWI immigrants.  Each of these groups has its own dynamics and own system that needs specific analysis.
 
6) Now that I explained the various types of immigrants coming to the US, let's get back to social class.  EWI immigrants, asylum seekers, refugees and many official immigrants do have higher rates of poverty than US native born population, but that is not the cause of poverty or social class in the US.  Instead, the middle class has been declining for 50 years.  Right after WWII, the US create GI Bill to help soldiers begin life after the war.  The GI Bill created low interest loans for college, mortgages, and small businesses. In order to pay for all of that, the marginal tax rate was 90% (compared to 35% today).  Ninety percent!  Many people who grew up in the 40s, 50s and 60s did not realize that American life was being fueled by high tax rates and government supported programs.  Then in the 1970s this began to change.  Wealthy think tanks convinced people that high taxes were bad.  This began a decades long decline in the middle class.  Most Americans saw their wages stagnate while the top 1% became incredibly wealthy.  This inequality between the middle class and the top Americans has been trending since 1970 steadily becoming more and more disparate. Without the help of government like we had in the 1950s, many essentials have become far more expensive such as healthcare, education, and housing.  All of this was happening regardless of any immigrant group coming to America. 
 
So, while considering social class, know that immigration status is one demographic that might affect a person's SES but that is only one aspect.  And by the numbers, there are far more Americans who were born here who live in poverty - more than 33 million Americans born in this country live in poverty and more than 50 million live in low income.  And like I explained above - the middle class has not kept pace with the wealthiest Americans so that group is a lot closer to the poorest Americans than it is to the wealthiest Americans.  And all of this is magnified by CA's high cost of living.  
 
I know this is long but I really wanted to help you understand both immigration and social class from a more nuanced perspective.