ADDING PRE-EMPTIVELY: I just re-read the OP and had originally thought it was from a non-US person, but now it seems to me that the OP is an American asking for clarification. Some of the below is really aimed at non-USians but rather than rewrite, let it stand as hopefully of some use. IANAL. IANA cop.
I feel fairly sure any respectably sized American city, whether in Colorado or not, has the ability to make its own laws (as long as these don’t conflict with state and federal law, though sometimes they do) and that these cities would have their own District Attorneys–for the non-USA readers, a District Attorney is the chief government prosecutor at a given level, which could be city, state, or even federal. The official name at the federal level is US Attorney for ___ District, meaning for a given area.
For example, the US attorney for the Southern District of New York State is one of the most powerful lawyers in the country, because the Southern District includes Manhattan, seat of financial power in the United States.
There are quibbles caveats and variations which I’m sure the real attorneys here can get into, but that’s the broad strokes.
As far as law enforcement, you’ll have city or local police, or sheriffs in “unincorporated” areas, which aren’t necessarily rural, and sometimes well-developed but smaller cities will contract with the county sheriff to provide law enforcement rather than provide their own police force. Many (most? all?) US states also have “state police,” who intervene in larger cases due to their resources, and who in some states also patrol large highways. Some states also have in addition a “Bureau of Investigation,” which is basically a unit that takes on really big cases like a multi-jurisditction serial killer, or state-level corruption.
At the federal level there are multiple enforcement agencies, but they don’t supersede each other necessarily–they sometimes cooperate, sometimes compete. The FBI is the biggest, with the widest reach, and perhaps the best; its remit only covers federal crimes though it often assists state or local agencies in difficult cases. Then you have assorted other specialized agencies like Immigration and Customs Enforcement, who are the guys who arrest and deport undocumented immigrants; the Bureau of Alcohol, Tobacco, and Firearms, a bizarre omnibus that investigates crimes relating to those three subjects; the Drug Enforcement Agency, which covers illegal drugs; and other agencies I’m not thinking of right now.