Refer to the current Denver sectional excerpt. A dashed line labeled "MODE C & ADS-B OUT" with a "30 NM" tick runs through this area. What does this boundary mark?

Why: This chart's own legend labels this boundary "MODE C (See FAR 91.215/AIM)," and the 30 NM figure matches § 91.215's 30-nautical-mile Mode C veil around a Class B primary airport, within which most aircraft must have an operating transponder with Mode C altitude reporting (14 CFR 99.13 separately requires ADS-B Out in the same area). This boundary is drawn well outside the Class B shelves themselves, which this excerpt also shows as the smaller "120/100"-labeled rings closer to the airport.

• The Mode C veil extends 30 NM from the primary airport, considerably farther out than the Class B shelves themselves — the two are not the same boundary, and this chart shows both separately.
• VFR flyways are marked with their own distinct symbol and labeled as flyways on sectional charts; this dashed 30 NM arc is explicitly labeled "MODE C & ADS-B OUT," not a flyway route.