State Laws as Extension of Federal Laws
States have the right to create their own laws which expand on Federal laws.
This has been done for many, many topics throughout all the 50 states.
Therefore, each state has the right to create its own laws which extend the Federal laws.
Federal law trumps State law
It is true, that Federal Law trumps state law. This means that if state law and federal law conflict, then federal law will control.
However, this does not mean that the federal law is absolute. States can write their own laws.
Federal Law as minimum/maximum; Yet state can extend
Federal law is set as a minimum level, or a maximum level (depending on the purpose of the law.)
However, the Federal Law is not an absolute law in a state.
Each state can make the minimum higher, or the maximum lower, as the state chooses.
As long as the state law does not go lower than the federal minimum (such as for the minimum wage), or exceed the federal maximum (such as for pollutants) then the state law is perfectly valid.
In fact, the state law, by extending the federal law, can make a better environment for the residents of the state.
Examples of State Laws Extending the Federal Laws
1. The minimum wage
The Federal Government sets a "minimum" for the minimum wage.
Yet, any state can raise its minimum wage to a higher value. Several states do indeed have a higher minimum wage than what the federal law stipulates.
2. Environmental control
The Federal Government sets a "maximum" for the levels of emissions (such as from a coal power plant.) This is the highest level allowed by the Federal government.
Yet any state can set stricter standards. This means that a state can lower the maximum level of that pollutant emitted within that state.
3. Criminal law (rights, due process)
The Federal Government sets a "minimum" level of rights for anyone arrested and prosecuted by the government for a crime.
Yet, any state can expand on these laws, allowing more rights, or greater due process, for a crime (state or federal crime) than what the minimum set by the federal government.