Could be one of several species, such as Sphaeralcea parvifolia or Sphaeralcea coccinea. Each has (typically orange) cup-shaped flowers in an upright cluster, each with five fully separated petals and a yellowish center. As far as I have seen, the globemallow species in Boulder are a few inches to a few feet tall, with grooved leaves. They seem to tend to grow in dry and often grassy areas.