Colleges will look at the grades on your high school transcript and the GPA that those grades earned. All grades are important but given you will be submitting applications in the fall of your senior year of high school, your grades from junior year will bear a lot of weight, as they are the most recent examples of your work.
If you started out high school with mediocre grades but finished strong with excellent marks, this improvement can be taken into consideration. It’s possible that schools with many highly qualified applicants will take a closer look a specific classes taken to try to glean if the student chose to challenge themselves in high school.