You have a mallow plant, genus Malva in the Malvacae family. Mallows look very much like geraniums, their leaves and flowers look quite similar.  However, when you take a closer look inside the flowers there are differences.  Mallows have a central drumstick-shaped column with fused staminal filaments, (like a hollyhock), that surround the pistil.  The mallow fruit looks a bit like a cheese round, giving the plant the name "Cheese weed". This article gives more information on mallow characteristics. Plants of the Mallow Family  http://www.wildflowers-and-weeds.com/Plant_Families/Malvaceae.htm.  Your specific mallow may be the common mallow, Malva neglecta or  Malva sylvestris  http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=282568&isprofile=0&, the wood or high mallow.

Geranium flowers follow the geranium (crane-bill) pattern with a single pistil surrounded with stamens.  The top of the pistil is narrow, and it widens down into the ovary.  As the pistil matures it looks like a crane's head.  The 10 stamens surround the pistil.  This article will allow you to compare geraniums and mallows,  Plants of the Geranium Family  http://www.wildflowers-and-weeds.com/Plant_Families/Geraniaceae.htm

Geraniums tend to grow and flower in the spring.  Mallows grow at this time of the year. 

Mallows are tough plants and form a tough tenacious tap root.  To control them remove them when they are small, before the root becomes woody.  They seem to be resistant to most herbicides.  They also readily reseed.