ALTON - This September, the Alton Amphitheater is inviting the community to slow down, gather with friends and family, and enjoy three Friday evenings filled with live music, local food and unparalleled sunsets over the Mississippi River.The 2026 Pop-Up Concert Series will take place Friday, September 4, September 11 and September 25 from 6-9 p.m., offering a relaxed atmosphere with regional live music, food vendors, yard games and plenty of room to spread out along Alton's scenic riverfront. Ad...